The common name tilapia hails from the name of the cichlid genus Tilapia. This genus used to be much bigger, but it has now been split into several different genera, e.g. Oreochromis and Sarotherodon. It is however still common to refer to the old members of the genus Tilapia as tilapias in everyday speech. The genus Tilapia belongs to the tribe Tilapiini in the subfamily Pseudocrenilabrinae. All species in the tribe Tilapiini are referred to as tilapiine cichlids.

The genus name Tilapia is a latinisation of the word thiape, which means fish in Tswana. Tswana (also known as Setswana) is a language belonging to the Bantu group of the Niger-Congo languages. Tswana is the national and majority language of Botswana.

The genus name Tilapia was introduced by Andrew Smith in 1840. Andrew Smith was a Scottish surgeon, explorer, naturalist and zoologist. At the age of 23 he was sent to Africa to supervise the medical care of European soldiers and soldiers of the Cape Corps.

Since tilapia is such a popular food fish, it has been ascribed with a specific name in many different languages and dialects. Tilapia is for instance known as amnoon (אמנון) in Hebrew and bolty (بلطي) in Arabic.   

In Ancient Egypt, the Nile tilapia was called ỉn.t and represented by its own hieroglyph. The hieroglyph is number K1 on the Gardiner's Sign List. (The Gardiner's Sign List is a list of common Egyptian hieroglyphs compiled by Egyptologist Sir Alan Gardiner.) When used as a logogram, the hieroglyph meant "a Nile tilapia". When used as a determinative (ideogram), it could refer not only to the Nile tilapia but also to flathead mullets, another group of important food fishes for the Ancient Egyptians. When used as a part of the phonogram, the hieroglyph represented the ỉn: sound.

In English, certain species of tilapia can be referred to as "St. Peter's fish". There is a passage in the New Testament where the apostle Peter (who would later become known as St. Peter) catches a fish in the Sea of Galilee that turns out to be carrying a shekel coin in its mouth. According to the legend, the fingerprints of Peter caused dark spots to appear on the sides of the fish. Dark spots on the sides of the body are a common trait in several species of tilapiine chiclids. The tilapia species living in the Sea of Galilee (which is actually a lake) is Sarotherodon galilaeus galilaeus.

When tilapia farming commenced in East Asia, new words for the tilapia fish in general and/or for certain types of tilapia appeared in many local languages and dialects. Tilapia is for instance known as ikan nila in Indonesia. Several Asian countries, including the Philippines, use the term pla-pla to denote large tilapia and reserve the name tilapia for small tilapias only.

In mainland China, tilapia is known as luofei (罗非鱼). This name is based on the origin of the Nile tilapia. The Chinese name for the Nile is niLOU and the name for Africa is FEIzhou. LOU + FEI = loufei. 

In Taiwan, tilapia is often referred to as “South Pacific Crucian Carp”, but there is also a Chinese word for the fish: Wu-Kuo (吳郭). This name is based on the surnames of Wu Chen-hui (吳振輝) and Kuo Chi-chang (郭啟彰), since they were the ones who introduced tilapia to Taiwan from Singapore.