Master - develop approach
Master and develop approach is a kind of a GIT repository workflow.
Instead of a single master branch, this workflow uses two branches to record the history of the project. The master branch stores the official release history, and the develop branch serves as an integration branch for features. It's also convenient to tag all commits in the master branch with a version number.
Mentioned means that development happens in two separate directions: master and development. Master could be also called production and development as a testing branch. Branch respectively means the independent clone of code (for a user it just means the program or client-software).