BitBucket [bɪtˈbʌk.ɪt]: A web-based hosting service to upload and share code. See also Github.

It runs on the Open Source version control system Git. Developers use version control systems to organize their projects, to update and change code and to store these modifications in a central repository. Others can contribute to that repository and download and upload changes.

Git is a command-line tool. It does not have its own user interface. You use it by entering short commands into the terminal/command-line. BitBucket is the webpage where developers store their project and network with the BitBucket community. Many Open Source projects are hosted on hosting pages like BitBucket so everyone can contribute, report issues and comment. But you can create private repositories where just a few invited people have access, too.