It's a way of distinguishing our own species, *Homo sapiens*, from the other members of the primate order.
Here's a breakdown:
* Primates: A large order of mammals that includes monkeys, apes, and humans.
* Humans: Belong to the family Hominidae, which is a part of the primate order.
* Nonhuman primates: All primates that are not humans. This includes gorillas, chimpanzees, orangutans, monkeys, and many others.
Therefore, the term "nonhuman primates" is a way to refer to all primates excluding humans.