Monkeys are haplorhine ("dry-nosed") primates, a paraphyletic group generally possessing tails and consisting of approximately 260 known living species. Many monkey species are tree-dwelling (arboreal), although there are species that live primarily on the ground, such as baboons. Most species are also active during the day (diurnal). Monkeys are generally considered to be intelligent, particularly Old World monkeys.
Lemurs are a clade of strepsirrhine primates endemic to the island of Madagascar. The word "lemur" derives from the word lemures (ghosts or spirits) from Roman mythology and was first used to describe a slender loris due to its nocturnal habits and slow pace, but was later applied to the primates on Madagascar. As with other strepsirrhine primates, such as lorises, pottos, and galagos (bush babies), lemurs share resemblance with basal primates.
Galagos, also known as bushbabies, bush babies, or nagapies (meaning "little night monkeys" in Afrikaans), are small, nocturnal primates native to continental Africa, and make up the family Galagidae (also sometimes called Galagonidae). They are sometimes included as a subfamily within the Lorisidae or Loridae.