Noun

(*plural* commutator lengths)

- The number of multiplicands needed, at a minimum, to express a given group element as a product of commutators.
*In , the commutator length of is two, since it equals but isn't a commutator.*

- The supremum, over all elements of a given group's derived subgroup, of their commutator lengths.
*The commutator length of is at least two, since there's an element of commutator length two in it.*