# Glossary A reference guide to terminology used in VitalSentinel and web performance monitoring. *** ## A [#a] ### Accessibility Score [#accessibility-score] A Lighthouse metric (0-100) measuring how accessible your website is to users with disabilities, including screen reader compatibility, color contrast, and keyboard navigation. ### Alert [#alert] A notification triggered when a monitored metric exceeds a defined threshold. Alerts can be Warning (potential issue) or Critical (urgent problem). See [Setting Up Alerts](/alerts/setting-up-alerts). ### AMP (Accelerated Mobile Pages) [#amp-accelerated-mobile-pages] A Google-backed framework for creating fast-loading mobile web pages. VitalSentinel can detect AMP pages through Google Search Console integration. *** ## B [#b] ### Best Practices Score [#best-practices-score] A Lighthouse metric (0-100) measuring adherence to web development best practices including HTTPS usage, no console errors, and correct image aspect ratios. ### Bounce Rate [#bounce-rate] The percentage of sessions where users leave after viewing only one page without any interaction. *** ## C [#c] ### CDN (Content Delivery Network) [#cdn-content-delivery-network] A network of distributed servers that deliver content to users from geographically closer locations, improving load times and reducing TTFB. ### Consent [#consent] User permission for data collection. VitalSentinel works without consent by default (no cookies), but persistent visitor tracking requires user consent for GDPR compliance. See [Data & Privacy](/others/data-privacy). ### CORS (Cross-Origin Resource Sharing) [#cors-cross-origin-resource-sharing] A security mechanism that controls how web pages can request resources from different domains. CORS errors can cause resource loading failures. ### CLS (Cumulative Layout Shift) [#cls-cumulative-layout-shift] A Core Web Vital measuring visual stability. It quantifies how much the page layout shifts unexpectedly during loading. Good: ≤ 0.1. ### Core Web Vitals [#core-web-vitals] Google's key metrics for measuring user experience: LCP (loading), INP (interactivity), and CLS (visual stability). These affect search ranking. See [RUM Monitoring](/features/rum-monitoring) and [CrUX Monitoring](/features/crux-monitoring). ### CrUX (Chrome User Experience Report) [#crux-chrome-user-experience-report] A public dataset from Google containing real-world performance data from Chrome users who opt into sharing statistics. Updated monthly. See [CrUX Monitoring](/features/crux-monitoring). ### Crawlability [#crawlability] The ability of search engine bots to access and index your website pages. *** ## D [#d] ### DNS Lookup [#dns-lookup] The process of converting a domain name to an IP address. Slow DNS can increase TTFB. ### Domain [#domain] A website address (e.g., example.com) that you add to VitalSentinel for monitoring. Each domain can have its own monitoring configuration. *** ## E [#e] ### E-commerce Tracking [#e-commerce-tracking] Automatic detection and tracking of online store events like product views, cart actions, and purchases. VitalSentinel auto-detects Shopify, WooCommerce, Magento, and Squarespace. See [Web Analytics](/features/web-analytics). ### Engagement Rate [#engagement-rate] The percentage of sessions with meaningful user interaction (scrolling, clicking, or spending significant time on page). See [Engagement Analytics](/features/engagement-analytics). ### Entry Page [#entry-page] The first page a visitor lands on when starting a session. Also called a landing page. ### Error Rate [#error-rate] The percentage of page views that include JavaScript errors. Used for RUM alerts. ### Evaluation Window [#evaluation-window] For Synthetic alerts, the number of recent tests to average when evaluating alert conditions (last 1, 3, 5, or 10 tests). ### Exit Page [#exit-page] The last page a visitor views before ending their session. *** ## F [#f] ### FCP (First Contentful Paint) [#fcp-first-contentful-paint] The time until the first text, image, or canvas element appears on screen. Indicates perceived loading speed. ### Field Data [#field-data] Performance data collected from real users visiting your site (e.g., RUM, CrUX). Compare with Lab Data. ### Form Factor [#form-factor] Device category used for filtering data. CrUX and RUM support Phone, Desktop, and All. Alerts support Phone, Desktop, or Any (all devices). *** ## G [#g] ### GA4 (Google Analytics 4) [#ga4-google-analytics-4] Google's current analytics platform that VitalSentinel can integrate with for traffic data. See [Google Analytics Integration](/features/google-analytics). ### GDPR (General Data Protection Regulation) [#gdpr-general-data-protection-regulation] EU privacy regulation governing data collection and processing. VitalSentinel is GDPR compliant by default with no-cookie tracking. See [Data & Privacy](/others/data-privacy). ### GSC (Google Search Console) [#gsc-google-search-console] Google's tool for monitoring search performance and indexing status. VitalSentinel integrates with GSC for indexing and keyword data. See [Google Search Console Integration](/features/google-search-console). ### gTLD (Generic Top-Level Domain) [#gtld-generic-top-level-domain] Common domain extensions like .com, .net, .org. VitalSentinel supports domain expiration monitoring for most gTLDs. *** ## H [#h] ### HTTP Status Code [#http-status-code] A three-digit response code from servers. 2xx = success, 3xx = redirect, 4xx = client error, 5xx = server error. Used in uptime monitoring. *** ## I [#i] ### INP (Interaction to Next Paint) [#inp-interaction-to-next-paint] A Core Web Vital measuring interactivity. It tracks the latency of all user interactions and reports the worst (or near-worst) interaction. Good: ≤ 200ms. ### Incident [#incident] A period when your site is down or unreachable. VitalSentinel tracks incident start time, end time, and duration. ### Indexing [#indexing] The process of search engines adding pages to their database so they can appear in search results. See [Indexing Monitoring](/features/indexing-monitoring). *** ## J [#j] ### JavaScript Error [#javascript-error] A runtime error in browser JavaScript code. VitalSentinel's RUM script automatically captures uncaught exceptions, promise rejections, and console errors. See [Error Tracking](/features/error-tracking). *** ## L [#l] ### Lab Data [#lab-data] Performance data from controlled synthetic tests (e.g., Lighthouse). Consistent but doesn't reflect real user conditions. Compare with Field Data. ### LCP (Largest Contentful Paint) [#lcp-largest-contentful-paint] A Core Web Vital measuring loading performance. It tracks when the largest content element becomes visible. Good: ≤ 2.5s. ### Lighthouse [#lighthouse] Google's open-source tool for auditing web page quality. VitalSentinel uses Lighthouse for Synthetic Monitoring. See [Synthetic Monitoring](/features/synthetic-monitoring). *** ## M [#m] ### Main Thread [#main-thread] The browser's primary execution thread for JavaScript, layout, and rendering. Long tasks on the main thread cause poor INP scores. *** ## N [#n] ### Network Requests [#network-requests] The total number of HTTP requests made when loading a page. A Synthetic monitoring metric – high request counts can slow page load. ### noindex [#noindex] A directive telling search engines not to index a page, using meta tags or HTTP headers. *** ## O [#o] ### Origin [#origin] The combination of protocol, domain, and port (e.g., `https://example.com`). CrUX provides origin-level and URL-level data. *** ## P [#p] ### P75 (75th Percentile) [#p75-75th-percentile] The value that 75% of measurements are equal to or better than. Used by Google for Core Web Vitals assessment. ### Page View [#page-view] A single instance of a page being loaded or viewed. The fundamental unit of web analytics measurement. ### Performance Score [#performance-score] A Lighthouse metric (0-100) summarizing overall page performance, weighted across FCP, SI, LCP, TBT, and CLS. ### PSI (PageSpeed Insights) [#psi-pagespeed-insights] Google's tool that combines Lighthouse testing with CrUX data. VitalSentinel synthetic tests run on PSI infrastructure. *** ## R [#r] ### Referrer [#referrer] The URL of the page that linked to the current page. Used to track traffic sources in Web Analytics. ### Render-Blocking [#render-blocking] Resources (CSS, JavaScript) that prevent the page from rendering until they're fully loaded. A common cause of poor FCP and LCP. ### Response Time [#response-time] The time taken for a server to respond to an HTTP request. Tracked in uptime monitoring. ### Rage Clicks [#rage-clicks] Rapid, frustrated clicking (3+ clicks in 1 second within 100px). Indicates UI issues or unresponsive elements. See [Engagement Analytics](/features/engagement-analytics). ### Rich Results [#rich-results] Enhanced search result formats like FAQs, recipes, or product listings, powered by structured data. ### robots.txt [#robotstxt] A file at your domain root that tells search engines which URLs they can crawl. See [Robots.txt Monitoring](/features/robots-txt-monitoring). ### RUM (Real User Monitoring) [#rum-real-user-monitoring] Collecting performance data from actual website visitors using a tracking script. Provides real-world insights. See [RUM Monitoring](/features/rum-monitoring) and [RUM Script Installation](/installation/rum-script). *** ## S [#s] ### Sample Rate [#sample-rate] The percentage of visitors whose data is collected by RUM. 100% tracks everyone; lower rates reduce data volume while maintaining statistical validity. ### Scroll Depth [#scroll-depth] How far down the page users scroll, measured as percentage milestones (25%, 50%, 75%, 90%, 100%). ### SEO Score [#seo-score] A Lighthouse metric (0-100) measuring search engine optimization factors like meta tags, crawlability, and mobile-friendliness. ### Session [#session] A single visit to your website. A new session starts after 30 minutes of inactivity. ### SI (Speed Index) [#si-speed-index] A Lighthouse metric measuring how quickly content is visually displayed during page load. ### Sitemap [#sitemap] An XML file listing your website's URLs to help search engines discover and crawl your content. ### Soft 404 [#soft-404] A page that looks like an error (thin content, "not found" message) but returns a 200 status code instead of 404. ### SPA (Single Page Application) [#spa-single-page-application] A web app that loads a single HTML page and dynamically updates content. VitalSentinel auto-detects SPA navigation via the History API. ### SSL/TLS [#ssltls] Encryption protocols that secure data between browsers and servers. Indicated by HTTPS and the padlock icon. ### Stack Trace [#stack-trace] A report showing the sequence of function calls that led to an error. Captured by RUM for JavaScript error debugging. ### Synthetic Monitoring [#synthetic-monitoring] Running automated tests from controlled environments to measure performance consistently. Compare with RUM. See [Synthetic Monitoring](/features/synthetic-monitoring). *** ## T [#t] ### Time on Page [#time-on-page] The duration a user spends on a page before navigating away. An engagement metric tracked by RUM. ### TLD (Top-Level Domain) [#tld-top-level-domain] The last part of a domain name (.com, .org, .co.uk). Some TLDs don't support WHOIS lookups for domain expiration monitoring. ### Traffic Source [#traffic-source] How visitors arrive at your site: Direct, Organic Search, Social, Referral, Email, Paid, or AI Search & Tools. ### TBT (Total Blocking Time) [#tbt-total-blocking-time] A Lighthouse metric measuring main thread blocking between FCP and TTI. Used as a lab proxy for INP. ### TTFB (Time to First Byte) [#ttfb-time-to-first-byte] Time from request start until the first byte of response is received. Indicates server responsiveness. ### TTI (Time to Interactive) [#tti-time-to-interactive] The time until the page is fully interactive and responds to user input within 50ms. *** ## U [#u] ### Uptime [#uptime] The percentage of time your website is accessible. 99.9% uptime = \~43 minutes downtime per month. See [Uptime Monitoring](/features/uptime-monitoring). ### URL Inspection [#url-inspection] A Google Search Console feature that checks the indexing status and issues for specific URLs. ### User-agent [#user-agent] In robots.txt, specifies which crawler a rule applies to (e.g., Googlebot, Bingbot, or \* for all crawlers). ### UTM Parameters [#utm-parameters] Tracking codes added to URLs (utm\_source, utm\_medium, utm\_campaign) to track marketing campaign effectiveness. *** ## V [#v] ### Viewport [#viewport] The visible area of a web page. Mobile viewport is smaller than desktop. ### Visitor [#visitor] A unique user identified by an anonymous visitor ID. Different from sessions (one visitor can have multiple sessions). *** ## W [#w] ### Web Vitals [#web-vitals] Google's initiative defining quality metrics for user experience on the web. Core Web Vitals are a subset used for ranking. ### WHOIS [#whois] A protocol for querying domain registration information. VitalSentinel uses WHOIS to monitor domain expiration dates (where available). ### Workspace [#workspace] An organizational container in VitalSentinel that holds domains, team members, and billing. Agencies typically use multiple workspaces for clients. See [Managing Workspaces](/workspace/managing-workspaces).