This entry is about a notion in category theory. For a different notion of the same name in (stable) homotopy theory see at Goodwillie calculus. The concept of a polynomial functor is a categorification of that of a polynomial. Polynomial endo-functors are used to encode a class of inductive types called W-types, and also as the underlying data of polynomial monads. Let be a locally cartesian closed category. A polynomial is a diagram in . These are also called bispans (cf. Elmanto & Haugseng)..