torsion subgroup
英[ˈtɔ:ʃən ˈsʌbɡru:p]美[ˈtɔrʃən ˈsʌbˌɡrup]
In the theory of abelian groups, the torsion subgroup AT of an abelian group A is the subgroup of A consisting of all elements that have finite order. An abelian group A is called a torsion (or periodic) group if every element of A has finite order and is called torsion-free if every element of A except the identity is of infinite order.