Firebase Authentication is a backend service provided by Firebase that allows you to authenticate users and manage user accounts in your app. It supports a variety of authentication methods, including email and password, phone number, and social media accounts such as Google, Facebook, and Twitter.

Firebase Authentication provides a set of APIs and SDKs that make it easy to add authentication to your app. It handles the heavy lifting of user management, including creating and managing user accounts, sending verification emails and SMS messages, and storing user data securely.

Firebase Authentication integrates with other Firebase services, such as Realtime Database and Cloud Firestore, allowing you to store and retrieve user data and control access to data based on the authenticated user. It also provides a number of security features, such as password hashing and multi-factor authentication, to help protect user accounts and data.

Overall, Firebase Authentication is a powerful and easy-to-use service for adding authentication to your app and managing user accounts. It can help you build a secure and scalable user management system for your app.