A familiar but respectful everyday way to refer to a Buddhist priest or monk. More formal writing may use 僧侶.
See also: 坊さん
法事にお坊さんを呼んだ。
We called a Buddhist priest for the memorial service.
We had the monk chant a sutra.
someone else's son
A familiar respectful term for another person's son, close to お坊っちゃん. This use can sound old-fashioned or very familiar in modern conversation.
See also: お坊ちゃん
Is your son already in elementary school?
He became a Buddhist priest after finishing university.
We had a priest chant a sutra at the memorial service.
お坊さん is a softer, slightly more polite everyday term for a Buddhist priest, while 坊さん is more blunt and casual.
お坊さん is the polite, respectful way to refer to a Buddhist priest, while 坊主 is the neutral or sometimes casual/derogatory term for the same person.