From Online Dictionary of Crystallography
Sous-groupe (Fr); Untergruppe (Ge); Subgrupo (Sp); Sottogruppo (It); 部分群 (Ja).
Let G be a group and H a non-empty subset of G. Then H is called a subgroup of H if the elements of H obey the group postulates.
The subgroup H is called a proper subgroup of G if there are elements of G not contained in H.
A subgroup H of G is called a maximal subgroup of G if there is no proper subgroup M of G such that H is a proper subgroup of M.