3-category
In mathematics, especially in category theory, a 3-category is a 2-category together with 3-morphisms. It comes in at least three flavors
- a strict 3-category,
- a semi-strict 3-category also called a Gray category,
- a weak 3-category.
The coherence theorem of Gordon–Power–Street says a weak 3-category is equivalent (in some sense) to a Gray category.