it is called the refractory period. Here is part of an article about this:
In men, erection subsides rapidly and the penis returns to its normal size. The scrotum and testes shrink and return to their unaroused position. Men typically enter a refractory period, during which they are incapable of erection and orgasm. The length of the refractory period depends on the individual. It may last for only a few minutes or for as long as 24 hours, and the length generally increases with age. Women do not appear to have a refractory period and, because of this, women can have multiple orgasms within a short period of time. Some men also experience multiple orgasms. This is sometimes related to the ability to have some orgasms without ejaculation.