In mathematics, in the field of group theory, a subgroup A {\displaystyle A} of a group G {\displaystyle G} is termed seminormal if there is a subgroup B {\displaystyle B} such that A B = G {\displaystyle AB=G}, and for any proper subgroup C {\displaystyle C} of B {\displaystyle B}, A C {\displaystyle AC} is a proper subgroup of G {\displaystyle G}. Wikipedia