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.
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.
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/
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