torsion

The term torsion is used for different concepts in different fields: In algebra, the torsion subgroup of a group is the group of elements of finite order (meaning: elements such that there is such that (with factors in the product)); similarly in ring theory an element of a module over a ring is a torsion element if it is annihilated by a nonzero element of the ring. A module is torsion (resp. torsion-free) if all its elements are torsion (resp. not torsion, except for zero). Classes of torsion.