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:
Mentioned above 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).
Master branch serves as a working software (or code). This branch stores tested and approved code and usually is delivered in releases.
Development branch is used for development purposes: this is a place where all new features, fixes appears first. Note that if a bug appears in the development branch, the production is not influenced by that. So mentioned approach minimizes the risks and costs of unsuccessful implementation.
Please note that use of GIT repository allows minimizing costs of unsuccessful implementation even in master code: it allows reverting the code to any previous versions, allowing so to revert incorrect changes (so production is back to a working state).
For more information, please use the full GIT repository manual on https://www.atlassian.com/git/tutorials/comparing-workflows/gitflow-workflow