Linked from
The 13 pages that link to Monoid, each with the reason it gives.
Identity elementRelated: A monoid makes the identity element part of its defining structure.
Ring (mathematics)Related: Ring multiplication is associative and may also have an identity.
CategoryRelated: A monoid is exactly a category with one object.
Inverse elementRelated: Monoids provide an identity, though not every element has an inverse.
Ring theoryRelated: A ring with identity has a multiplicative monoid.