na-adjective, noun
Describes a person who readily engages in conversation, often with a positive or neutral connotation of being sociable and good at keeping a conversation going. The term is somewhat dated and less common in modern casual speech.
彼は口まめで、初対面の人ともすぐに打ち解ける。
He is talkative and quickly gets along even with people he meets for the first time.
祖母はとても口まめで、近所の人たちとよく立ち話
My grandmother is very chatty and often stands around talking with the neighbors.
Compound of 口 (mouth, speech) and まめ (diligent, faithful). The original sense is 'diligent with one's mouth', i.e., always ready to talk. The kanji spelling 口忠実 reflects this etymology but is now rare.