What are the criteria for calling someone a high or low capacity?

Some Buddhist teachers and writings I have seen differentiate between (students of) “high capacity” and “low(er) capacity”. As far as I’ve understood, some of the criteria for saying that some people are of “high capacity” is intelligence and morality. It also seems to me that you actually have to have heard about the Dharma to be of “high capacity”. Can someone give explicit criteria for what “high capacity” and “low(er) capacity” actually means? Or a reference to an explanation?