Apart from what WJW said, it's not an objective criterion but it essentially means that you don't lose out in terms of initiative or position. A counterexample

Apart from what WJW said, it's not an objective criterion but it essentially means that you don't lose out in terms of initiative or position. A counterexample might be accepting the queen's gambit with black (i.e. 1. d4d5 2. c4cxd4), that way you win a pawn but you arguably give white an advantage in development (an in many cases white will be able to recapture the pawn as a result)