http://dhamma.t3x.org/vaca.html
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Vācā ("speach") is mostly mentioned in relationship with the Noble Eightfold Path (as "right speach") and the precepts. In the precepts, it means "not to say what is not true", but the eightfold path develops the principle further than that. It discourages slanderous speech, every kind of harsh speech, gossiping, and idle chatter.
Some of these kinds of talking are accepted or even expected behavior in our culture. Portraying people in a light that makes them seem inferior or exchanging meaningless anecdotes about them is a valued pastime. In general, "passing time" by chatting is something that every adult is expected to take part in.
More than often this kind of talk will agitate the participants, though, lead to competition, where everybody only waits for their time to talk, and leave them in a excited (and hence deluded) state of mind, even when the conversation finishes.
Proper speech should convey useful information. It should criticise only to help the recipient improve their life or that of the community in which they live (which is ultimately the same thing). As a rule of thumb, any conversation that does not lead to agitation is probably right speech.