The Firebase Realtime Database is a cloud-hosted NoSQL database that lets you store and sync data between your users in realtime.The Firebase Realtime Database lets you build rich, collaborative applications by allowing secure access to the database directly from client-side code. Data is persisted locally, and even while offline, realtime events continue to fire, giving the end user a responsive experience.When someone sends you a message in a chat app, and you receive that message on your phone, or you get a push notification, that notification or message is received in 'realtime. 'A real-time application (RTA) is an application program that functions within a time frame that the user senses as immediate or current. The latency must be less than a defined value, usually measured in seconds. ... The use of RTAs is called real-time computing (RTC).Firebase is one kind of NoSQL database. The Firebase database is just a big JSON object where you can store whatever you want inside. Unlike SQL there's no schema for the database, no tables, no columns, it's just a combination of key/value pairs.