What does the idiom quick mean?

The idiom "quick" isn't a true idiom. It's simply the adjective "quick", which means:

* Happening or done with speed: "He made a quick decision."

* Short in duration: "It was a quick meeting."

* Moving or acting rapidly: "She is a quick learner."

Perhaps you're thinking of a different phrase or idiom that includes the word "quick"?

If you can provide more context or the phrase you're thinking of, I can help you understand its meaning!