A very young monkey, like a very young human being, is called an "infant." Sometimes the young of apes are also called "babies," reflecting the close genetic relationship between apes and humans and the many similarities between our young.
Slightly older monkeys, developmentally similar to a human toddler, child or teenager, are not given special terms. Past infancy, a monkey is referred to by its gender, male or female, with modifiers such as "sexually mature," "adolescent" or "pre-adolescent" to indicate its age. Some primates, such as orangutans, often experience growth spurts after reaching sexual maturity. In this case, older monkeys that have not yet fully matured are referred to as "subadults."