GitHub is a website which uses Git software to host project repositories online. It is the largest source code host in the world by a large margin, hosting over 38 million projects at time of writing. It is strongly associated with Git itself and a major reason for Git’s popularity.
Github is most well-known for hosting open source projects publicly, though you can also buy private repository hosting. GitHub repositories can be used as a dumping ground for code or as the gathering place for a team working on a project together.