1. Of middling quality; neither bad nor good, average; so, contextually, indifferent, of poor quality, second-rate.
2. Used chiefly of literary or artistic works, ability, or knowledge, and hence of people considered with regard to their average mental power or skill.
3. Etymology: in general, borrowed from Middle French mediocre, learned borrowing from Latin mediocris of "middle height, in a middle state" or by extension, "moderate quality"; originally, "halfway up a mountain" (medius, "middle" + ocris, "jagged mountain" or "rough stony mountain").