1.NounA group G which is part of a finite chain Gi (0 ≤ i ≤ n) of subgroups, where G0 is the trivial subgroup and Gn = G, such that each intermediate subgroup Gi is a normal subgroup of the next in the chain (i.e., Gi ◁ Gi+1) and each quotient Gi+1/Gi is a cyclic group.