Firebase is a platform developed by Google for creating mobile and web applications.
It is now their flagship offering for app development.
More technically, Firebase is a BAAS short for Backend-as-a-service which helps you to build better apps, websites, or games regardless of server-side coding, API or backend data storage.
Firebase Realtime Database
Firebase offers two databases: Cloud Firestore and Firebase Realtime Database, which are NoSQL, cloud, realtime database.
All of the data, products, and services on Firebase are backed by Google components.
This means that there is no need for any middleware: the client SDKs offered by Firebase communicate with these Google backend services.
Data is synced across all clients in realtime, and remains available when your app goes offline.
Data is stored as JSON and synchronized in realtime to every connected client.