What is the practice of a man having several wives known as?

The correct answer is Option (3) → Polygyny

Polygyny is the practice of a man having several wives.

Option 1- Endogamy refers to marriage within a unit- this could be a kin group, caste, or a group living in the same locality.
Option 2- Exogamy refers to marriage outside the unit.
Option 3- Polygyny is the practice of a man having several wives.
Option 4- Polyandry is the practice of a woman having several husbands.