Guv is a British way for a man to speak to another man, especially a customer. A taxi driver might say, “Where to, guv?” A shop worker might say, “That’s six pounds, guv.” It is friendly, informal, and a little old-fashioned. You hear it most in England, especially London, and mostly from men talking to men.

It is a spoken short form of gov, and gov is short for governor. In older British talk, governor did not only mean the person who runs a place; it was also a way to say “boss” or “sir”. Guv’nor is the longer chatty form. People also call their own boss “the guv’nor”.

You would not use this with a woman in the same way, and you would not use it in Taiwan or in American English — it would sound as if you were putting on a British character.