expression, ichidan verb
throw in a suggestion; put in one's two cents; interject
Used when someone offers an opinion or suggestion in a conversation, often casually or without being asked. Can carry a slight nuance of butting in.
会議で彼はよく口を入れる。
He often throws in suggestions during meetings.
二人の話に口を入れるのは
I'll refrain from butting into their conversation.