Don't chatter idly during the meeting.
He's always just talking nonsense, so work doesn't progress.
おしゃべり is neutral or positive chatting, while 無駄口 emphasizes useless or time-wasting talk.
雑談 is casual conversation or small talk, not necessarily negative; 無駄口 implies the talk is pointless.
Standard kanji spelling.
Variant with katakana ムダ; seen in casual writing.
Rarely used kanji form.
Compound of 無駄 (むだ, 'useless') and 口 (くち, 'mouth'), with rendaku voicing of くち to ぐち.