A monkey is any cercopithecoid (Old World monkey) or platyrrhine (New World monkey) primate. They have four limbs. You could say that they have four legs, though, since they don't walk upright like we do most of the time, it isn't quite the same!
New World monkeys are the five families of primates that are found in Central and South America and portions of Mexico: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Platyrrhini parvorder and the Ceboidea superfamily, which are essentially synonymous since Ceboidea is the only living platyrrhine superfamily. They differ from other groupings of monkeys and primates, such as the Old World monkeys and the apes. Monkey
Cercopithecinae - 12 genera
Colobinae - 10 genera
The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade (or parvorder) of Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous terrain, and are also known from Europe in the fossil record. However, a (possibly introduced) free-roaming group of monkeys still survives in Gibraltar (Europe) to this day. Old World monkeys include many of the most familiar species of nonhuman primates, such as baboons and macaques. Primate