What does "natural son" mean?

A male biological offspring, whether legitimate or illegitimate, as opposed to one adopted.

Natural son

noun

noun ·Rare ·Advanced level

Noun

1
A male biological offspring, whether legitimate or illegitimate, as opposed to one adopted.
"They have two children: a natural son and an adopted daughter."
2
An illegitimate son.

"They have two children: a natural son and an adopted daughter."