Firebase is a hosted infrastructure tool made by Google. It allows you to focus just on developing real-time applications for web and native iOS/Android.
They have an SDK for iOS, Android, and The Web. As well as a Node.js, C++, and Java. You can find their Extensive reference here https://firebase.google.com/docs/reference/
Not only does Firebase allow you to store real-time data. It also allows you to use the integrated Storage, Hosting, Cloud Messaging, Authentication, Test Lab, Crash Reporting and AdMob services.
Terms and Conditions can be located here https://firebase.google.com/terms
These terms are governed by Google's Developer Terms of Service https://developers.google.com/terms