Subgroup of prime index

Symbol-free definition
A subgroup is said to be of prime index in a group if its index in the whole group is a prime number.

Definition with symbols
A subgroup $$H$$ of a group $$G$$ is said to be of prime index if $$[G:H]$$ is a prime number.

Stronger properties

 * Subgroup of index two

Weaker properties

 * Maximal subgroup
 * Subgroup of finite index
 * Seminormal subgroup