Popular within many open source projects but not only.

Master branch of a specific location (Github, Gitlab, Bitbucket, local server) contains the latest shippable version. For each new feature/bug fix/architectural change each developer creates a branch.

Changes happen on that branch and can be discussed in a pull request, code review, etc. Once accepted they get merged to the master branch.

Full flow by Scott Chacon:

• Anything in the master branch is deployable
• To work on something new, create a descriptively named branch off of master (ie: new-oauth2-scopes)
• Commit to that branch locally and regularly push your work to the same named branch on the server
• When you need feedback or help, or you think the branch is ready for merging, open a pull request
• After someone else has reviewed and signed off on the feature, you can merge it into master
• Once it is merged and pushed to ‘master’, you can and should deploy immediately

Originally presented on Scott Chacon’s personal web site.

Image courtesy of the GitHub Flow reference