The Vietnamese word "bàu nhàu" means to grumble or growl. It describes a sound or expression of dissatisfaction, often done in a low voice or in a way that shows annoyance or displeasure.
While "bàu nhàu" primarily means to grumble or growl, it can also imply a sense of whining or complaining in a more general sense. The focus is on the dissatisfaction rather than an outright protest or loud complaint.