If you find yourself stuck on a bus beside someone who talks endlessly about boring subjects, you might think to yourself, "What a windbag." It's an informal way to describe a big talker.
The word windbag is a useful but derogatory way to talk about a boring chatterer. A windbag might gossip, or brag, or tell a long story — but in any case, nothing he says is interesting or useful information. The original fifteenth century meaning of windbag was "bellows for an organ," which was literally a bag of wind or air. By the early 1800s, it took on the metaphorical meaning of "person who talks too much."