Github
Github is a cloud where developers can save code.
Using git as a base, developers can safely store their code (and the history of all its various versions) in the cloud where they can get to it from different computers and share it with others.
What's the difference between git and GitHub?
git is a low level tool that developers use to keep track of code. They can use it to manage history, merge code, and do a lot of other stuff.
GitHub is where all of that history gets stored in the cloud.