Interjection
(idiomatic) An expression used to concede a point; denotes that, upon consideration, something is correct or reasonable; an expression of acknowledgment or understanding.
Synonym: very well
You can play the exercises pretty well on piano, fair enough, but can you play the movement expressively?
Used to stop somebody talking or an argument, other synonyms include that's enough, that'll do.
Source: en.wiktionary.org