Active Directory (AD) is Microsoft's directory service for managing users, computers, permissions, and other resources within a Windows network. It provides administrators with a centralized way to authenticate users, control access to resources, apply security policies, and manage devices across an organization.

A backend server is a server that handles the behind-the-scenes processing required by a website, application, or online service. It receives requests, executes application logic, communicates with databases or other services, and returns the required data to the frontend. Users normally do not interact directly with a backend server. Instead, they interact with a website or application interface, while the backend processes tasks such as user authentication, database queries, payments, file operations, and API requests.

Backup retention refers to how long backup copies are kept before they are deleted, overwritten, or moved to long-term storage. A backup retention policy defines which backups should be retained and for how long, helping organizations maintain useful recovery points without storing every backup indefinitely.