In mathematics, and particularly in category theory, a polygraph is a generalisation of a directed graph. It is also known as a computad. They were introduced as "polygraphs" by Albert Burroni and as "computads" by Ross Street.
In the same way that a directed multigraph can freely generate a category, an n-computad is the "most general" structure which can generate a free n-category.
References
Polygraph (mathematics) Wikipedia(Text) CC BY-SA