As Wikipedia describes Configuration Management:
is a systems engineering process for establishing and maintaining consistency of a product's performance, functional, and physical attributes with its requirements, design, and operational information throughout its life.
For example this technical article discusses Configuration Management with Git and Puppet, introducing:
When working in a larger environment, using a central configuration management environment allows you to quickly rebuild vital systems or create copies, as well as keep track of your inventory and services. By centralizing all information, decisions and impact analysis can be done quickly and efficiently.
Github is a free and commercial service for hosting software versions for packaging, distribution and re-updating, that has become so popular as to be considered a de facto standard.
A particularly helpful use case introduction is this scenario published by Flickr - Configuration management for distributed systems (using GitHub and cfg4j).