What is the difference between "mad " and "angry"?

The term 'mad' refers to mentally unstable person (insane) or someone that is extremely enthusiastic or even crazy about someone or something.
To be 'angry' just means to feel or display strong annoyance, irritation, anger.

It is common in informal everyday expressions (especially in AmE) for the word "mad" to be used for "angry" or "very angry". They are sometimes used interchangeably in this context (angry with somebody/mad at somebody; angry about something/mad about something). 'Mad' is a little stronger than 'angry' when it comes to their intensity.

However, both terms carry other meanings:

- "mad", in informal BrE, means extremely foolish idea or behaviour (Americans in this context use 'crazy'), e.g.' You're mad to meet with your father's friend!
- In slang, "mad" is used to say that something is excellent, great wonderful, frivolous, e.g. "We're gonna have a mad time tonight!". It means ' a lot' or 'extremely' as well. ("She's mad cool", "There were mad people at the party!").

- "Angry", on the other hand, also means 'stormy' (in literary context) or 'painful'.

You can look it up in dictionaries ;-)