YAML, YML

• YAML

Yet Another Markup Language, a digestible data serialization language that is often utilized to create configuration files and works in concurrence with any programming language. It’s a strict superset of JSON, so it can do everything that JSON can and more. 

 

• YML

For historic reasons, many Windows programmers are still scared of using extensions with more than three characters and so opt to use .yml instead.

reference : circleci.com/blog/what-is-yaml-a-beginner-s-guide/