What is the term used for a marriage within kin group, caste, or a group living in the same locality?

Endogamy

The correct answer is Option (4) → Endogamy

Endogamy refers to marriage within a unit- this could be a kin group, caste, or a group living in the same locality.

Remaining Options:

Polygyny is the practice of a man having several wives.
Polyandry is the practice of a woman having several husbands.
Exogamy refers to marriage outside the unit.