Firebase is a Backend-as-a-Service(BaaS) which started as a YC11 startup. Firebase has a real-time database that allows storing a list of objects in the form of a tree. We can synchronize data between different devices.

Google Firebase is Google-backed application development software which allows developers to develop Android, IOS, and Web apps. Firebase provides several tools for reporting and fixing app crashes, tracking analytics, creating marketing, product experiments and much more.

Firebase has plenty of features that can be used to integrate in any applications making the backend work easiar.

Firebase can be implemented in iOS, android and web apps with few lines code and the the data can be synced across all the platform in real time.

• Authentication: You can setup authentication with google, facebook, github custom email/password, phone OTP verification and much more service providers with simple lines of code without worrying about how it basically works in the backend.
• Firestore: Cloud Firestore is a flexible, easy to use and a scalable NoSQL cloud database. It syncs the data acroos all the platform in realtime which triggers the changes in the app without the need of refreshening.
• Cloud Storage: It is a storage bucket generally used to store photos, videos and files. It allows us to upload and download files from mobile clients through the Firebase SDKs, and perform server-side processing such as image filtering or video transcoding using the Google Cloud Platform.
• Hosting: Firebase Hosting allows fast and secure hosting for our web application, static and dynamic content, and microservices. It is production-grade web content hosting for the developers. We can easily and quickly deploy web apps and serve both static and dynamic content to a global content delivery network with only a single command.
• Cloud Functions: Cloud functions for firebase enable us to automatically execute the backend code in response to events triggered or caused through HTTPS requests and Firebase features. We can send push notifications to users, integrate third party library, execute intensive tasks in the backend and there is no need to maintain our own server.

You can manage user's data, app's performance & growth, analytics, ads etc all in your frontend code. There are many more powerful features provided by firebase which is very easy to use and boosts the performance of your app.

To explain in simple words, you can use firebase as a backend service in your frontend work. With simple syntaxes you can replace all the backend code(like routing, fetching and sending response from backend).