Refers to a male child, often specifically the eldest son in a family. The 'eldest son' nuance is common in formal or traditional contexts.
He is the father of one boy and one girl.
一男として家を継ぐ責任がある。
As the eldest son, he has the responsibility to succeed the family.
The couple had a son in their fifth year of marriage.
They were blessed with a son and a daughter.