We say social, because CodePen is a community. Most creations on CodePen are public and open source. They are living things that other people and the community can interact with, from a simple hearting, to leaving a comment, to forking and changing for their own needs.
People use CodePen for all sorts of things: prototyping new ideas, reduced test cases for bugs, sending clients things to look at, evaluating potential hires, to finding inspiration. People also use CodePen as a sort of resume and portfolio, showing off their best design and development work.
We're trying to make CodePen a happy and healthy place for front-end designers and developers and the people looking for them, while also being a damn fine place to code. ❤️