This phrase is wonderfully flexible. 不错, pronounced bùcuò, literally means 'not bad' or 'not wrong' depending on the context but can also be used to mean 'pretty good'.
Examples:
-你的答案不错 (Your answer is correct.)
-A.我听说你会说中文？ B. 不错.
(A. I heard you can speak Chinese? B. Yes. (You're not wrong.))
-这个主意不错. (This idea is not bad).