Neutral term for a man who is married. Often used in contrast with 未婚男性 (unmarried man).
He is a married man with two children.
This survey targets married men.
未婚男性 means 'unmarried man', the direct opposite of 既婚男性.
既婚女性 means 'married woman', the female counterpart.
Compound of 既婚 (kikon, 'married') and 男性 (dansei, 'man'). 既婚 is itself from 既 (already) and 婚 (marriage).