Colloquial refers to the level language is used in everyday speech. Slang is a sub-category of colloquial expressions.
However, familiar colloquial words are much more free and careless.
Examples:
COLLOQUIAL: SLANG FAMILIAR COLLOQUIAL (MEANING)
1. dude guy, bro, buddy friend
2 score grab purchase
3. sawbones doc doctor, surgeon
4. ain't ain't am/are/is not
5. but t bum buttocks
