Not shown to be true, and not yet shown to work. Those are two uses worth separating. In law and argument it means a claim that nobody has proved — "the allegations remain unproven" — and here the important point is that unproven does NOT mean false. It means we do not know. Newspapers rely on this word for exactly that reason: it lets them report an accusation without saying the person did it. The second use is about ability and reliability: an unproven technology, an unproven player, an unproven method. Here it means "has not yet been tested enough for us to trust it" — no accusation at all, just caution, and often with a hopeful edge, because unproven things are frequently new things. Both uses are formal-ish; you will meet them in news, business and science writing far more than in chat. Spelling note: `unproved` also exists and means the same, but `unproven` is much more common now.