The term "lesser ape" refers to a group of primates that are smaller and less intelligent than the great apes, such as chimpanzees, gorillas and orangutans. The term has become outdated as it is considered to be a derogatory term, hence there are alternative synonyms that are more acceptable and useable. These include the gibbons, siamangs, and hylobatidae. Gibbons are known for their long arms and acrobatic skills when swinging through trees. Siamangs are a larger species of gibbon with a unique vocal ability that allows them to communicate over long distances. Hylobatidae is another term used to refer to these primates, which includes the previously mentioned gibbons and siamangs.