Linked from
The 16 pages that link to Coset, each with the reason it gives.
Finite groupRelated: Cosets partition finite groups and underpin Lagrange’s theorem.
SubgroupRelated: Cosets partition a group according to a chosen subgroup.
Quotient ringRelated: Each quotient-ring element is a coset of the defining ideal.
Cayley graphRelated: Cosets can index vertices in related graphs built from group actions.
Conjugacy classRelated: Class sizes are indices of centralizers, hence counts of cosets.