I agree, it is vague because it's baseball and everything is relative. Is a .300 hitter a good hitter? Is a .299 hitter not a good hitter? Where is that line then? We're even unable to define with any certainty exactly how large a sample has to be in order to not be "small".
What I believe is that some players are better at getting hits in clutch situations than other players are and those are the players I refer to as being "clutch".
BTW, I also believe in the soul, the small of a woman's back, the cock, the pussy, the hanging curve ball, high fives, good scotch...