What is the difference between slang and colloquial?

Answer 1

Colloquial (adjective) means pertaining to common/ordinary/everyday or familiar conversation, not formal, academic or literary.

It can be used to describe terms used in normal discourse between people of a particular language group. In many languages there are colloquial phrases and expressions, and many of these may not be listed in standard dictionaries. However, they are often used, and everyone knows what they mean. [Etymology: Colloquial is from colluquy, Latin colloquium, from con, with, + loquor, to speak]

Examples of colloquial language: 'We must get someone in to help us balance the books. Do you know a good accountant?" "It's no good leaving her a message to phone you back. You can wait until the cows come home and she'll never call!"

Slang (noun) refers to words, phrases and uses of language that are considered to be very informal and the usage is often restricted to special contexts or is only used by a particular class, profession, social group, etc. e.g. prison slang, or in speech by people who know each other well.

Some slang includes abusive, offensive or vulgar langauge and 'taboo' words.

Most slang expressions are spoken, not written and would be considered inappropriate in formal types of communication.

Examples of slang "We get smashed (drunk) every Friday night." "We've all had this bug (illness) for a week."

Colloquialisms are the broad category of informal speech which includes slang. Slang is a sub-category of Colloquial expressions.
No, there is a slight difference. Colloquialism is when a word is used in informal or relaxed use. Most native speakers will know what a colloquial word means. Slang is when a word is used by a small group of people, e.g. teenagers, which is not used by most people.

A common example of colloquialism is the word "cool''. Cool can be found in the dictionary and everyone knows what it means. However, a person would not use "cool" when writing an article or a paper. The ironic thing is that in the 1960's, cool was slang only hippies knew what the word meant.

Answer 2

None - they mean the same thing.