Someone who is mad has a mind that does not work in a normal way, with the result that their behaviour is very strange.

You use mad to describe people or things that you think are very foolish.

If you say that someone is mad, you mean that they are very angry.

If you are mad about or mad on something or someone, you like them very much indeed.

Mad behaviour is wild and uncontrolled.

If you say that someone or something drives you mad, you mean that you find them extremely annoying.

If you do something like mad, you do it very energetically or enthusiastically.