Simplicial Sets

Recall the definition of the simplex category:

Transclude of finite-sets-category#^cf602c

Simplicial Set

A simplicial set is a functor ${\mathsf{\Delta }}^{\text{op}}\to \mathsf{Set}$.

e.g.

References

Simplicial Sets vs. Simplicial Complexes
Turning simplicial complexes into simplicial sets