Perfect competition. In the short term, such markets are productively inefficient as output will not occur where marginal cost is equal to average cost, but allocatively efficient, as output under perfect competition will always occur where marginal cost is equal to marginal revenue, and therefore where marginal cost equals average revenue. However, in the long term, such markets are both allocatively and productively efficient.
Which term best describes Perfect Competition?
That was the correct answer, well done! 
Sorry, that was the wrong answer 