the term ape is commonly used to refer to monkeys or the great apes, or some combination thereof. As it happens though, biologists have assigned a specific meaning to the word ape. Apes are members of the Superfamily of Hominoidea, the hominoids.
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorrhini
Parvorder: Catarrhini
Superfamily: Hominoidea
Apes include the gibbons and the great apes. They are tailless, although most of them are avid climbers, and have long arms and specially adapted wrist joints to help them swing through the trees. They are generally omnivores, often with a preference for fruit and leaves. They are native to Asia and Africa, and with one notable exception are currently suffering from reduced habitat and populations.
If you have an unidentified Catarrhini, the preferred method of determining whether it is an ape or an old world monkey is to (very carefully) look at its molars. The old world monkeys have bilophodont molars, with even, parallel sets of cusps. Apes have the Y-5 molar pattern, five cusps, three on one side and two on the other. (The valley between these cusps have a 'Y' shape, hence Y-5).