> ## Documentation Index
> Fetch the complete documentation index at: https://docs.flashduty.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Glossary

> This document details the key terms and concepts used in RUM to help users better understand and use RUM features.

## Core Concepts

| Name                           | Description                                                                                                                                                                                                 |
| ------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **RUM (Real User Monitoring)** | RUM (Real User Monitor) helps developers understand actual user experience and optimize application performance by collecting and analyzing performance data from real users using websites or applications |
| **Session**                    | Sessions are the core unit of RUM data aggregation, used to analyze user journeys and experiences                                                                                                           |
| **View**                       | Views record page load times, resource requests, etc., core to performance monitoring                                                                                                                       |
| **Action**                     | Used to analyze user behavior, measuring interaction performance and frustration points (such as "rage clicks") in user experience                                                                          |
| **Resource**                   | Analyze resource loading times and performance to optimize page load speed                                                                                                                                  |
| **Error**                      | Used to monitor frontend stability and identify errors affecting user experience                                                                                                                            |
| **Long Task**                  | RUM captures long tasks to identify performance bottlenecks causing page stuttering or poor user experience                                                                                                 |
| **Pageview**                   | Pageviews are the basic unit of RUM data, used to analyze the performance of specific pages                                                                                                                 |
| **Issue**                      | Issues are the core of error management, used to aggregate similar errors, prioritize problems, and combine context to help developers quickly locate and fix issues                                        |

## Performance Metrics

| Name                               | Description                                                                                                                            |
| ---------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------- |
| **Core Web Vitals**                | RUM monitors these metrics to evaluate webpage loading and interaction performance                                                     |
| **LCP (Largest Contentful Paint)** | Measures page loading performance, recording the time when the main content of the page finishes loading                               |
| **FID (First Input Delay)**        | Measures page interaction performance, recording the delay from when a user first interacts with the page to when the browser responds |
| **CLS (Cumulative Layout Shift)**  | Measures page visual stability, recording unexpected layout shifts that occur during page loading                                      |
| **TTFB (Time to First Byte)**      | Measures server response speed, recording the time from when the request is sent to when the first byte is received                    |

## Data Analysis

| Name               | Description                                                                              |
| ------------------ | ---------------------------------------------------------------------------------------- |
| **Facet**          | Facilitates building queries in RUM Explorer to analyze behavior of specific user groups |
| **Attribute**      | Provides context and enhances data analysis flexibility                                  |
| **Global Context** | Enhances customization capabilities for RUM data analysis                                |