In the US, there is no difference. "Faucet" is used more commonly. Ian is exactly correct about tap water. I could be wrong but I think that possibly "tap" means "the place where water can come out of a pipe," while "faucet" means "the device, including the handle and the valve, that controls the flow of water at a tap."

I will add that in the U.S. we call water that comes out of the faucet "tap water." For example: Do you want to drink bottled water or is tap water okay?

In the US, we usually use the word faucet. In British English. tap is sometimes used. They can mean the same thing. If you are referring to the the details of plumbing, they are different terms.

They're the same thing. Faucet is generally preferred in American English, although many Americans also say tap. Tap is preferred in the UK. If I'm not mistaken, they don't say faucet very often in the UK. However, they mean exactly the same thing.