Git is a version control system for tracking changes in computer files and coordinating work on those files among multiple people. -Wikipedia
Git is basically a version control tool to avoid version conflicts on the projects I create and those I colloborate on. Let's get on the same page.
Git runs in the background of the local system. Github is a service which serves as a remote repository of various gits on a centralized website.
GItGub Enterprise is a subscription version of GitHub which provides organizations a private, secure platform to collaborate internally.