A set of classes that together include all nouns is classified as gender. The most familiar sets of genders are of three classes as masculine, feminine, and neuter.
Masculine nouns refer to the male member of a species (i.e. man, boy, actor, horse, etc.)
Feminine nouns refer to female members of a species (i.e. woman, girl, actress, mare, etc.)
Common nouns refer to members of a species and don't have specific gender (i.e. parent, friend, client, student, etc.)
Neuter nouns refer to things that have no gender (i.e. rock, table, pencil, etc.)