In my opinion, slang is the street language, not everybody understands it and you will probably not find the words in a regular dictionary. Colloquial is the not so formal way of talking. It’s the way most people talk, unless they want to be formal or technical.
I hope I was helpful.
While it is not always rude, most people find slang somewhat indelicate. Colloquial is just informal.
Slang is usually confined to certain groups within society and would have to be explained more often than colloquial, which is usually just poorly spoken language.
I think a handy guide might be to think of colloquial as being bad grammar and to think of slang as being bad language.
Colloquial words are more common in informal spoken English . Slang words are very informal or restricted to a particular social group as Maxiogee has mentioned , and it should be distinguished from coarse slang which indicates a word that, although widely found, is still unacceptable to many people.