Branch devel: devel branch is the default branch in Galaxy repository. It is used as a primary merge target for all feature and bugfix pull requests.
Branch master: master branch points to the latest release version, which is running on the Galaxy website.
Release branches: Release branches release/x.x.x, where x.x.x is for the next release version, are used for release preparation. Pull requests that are intended to be released as a part of the next release version should be merged to the release branch following the Release process.