child born out of wedlock; illegitimate child
Legal and social term for a child whose parents were not married at the time of birth. 'Love child' is a softer, sometimes euphemistic gloss, but the core meaning is legal illegitimacy.
Discrimination against children born out of wedlock is prohibited by law.
He was born out of wedlock, but his parents later married.
A more formal legal term for an illegitimate child, often used in legal contexts.
Compound of 婚外 (こんがい, 'outside marriage') + 子 (し, 'child'). The term is a straightforward Sino-Japanese construction.