Etymology: from thiape, the Tswana word for fish (Tswana is also known as Setswana and is the national language of Botswana).
The genus name was introduced by Scottish surgeon/explorer/zoologist Andrew Smith in 1840.
Tilapia fish are disease-resistant, prolific, and adaptable. They can live in brackish water and in oxygen-deficient water as long as it is warm enough, and can survive on algae, plankton, larval fish, detritus, and even human waste. Because of their tolerance and their efficient food utilization, the fish can be farmed in very high concentrations.
In case you're worried, it's unlikely that your dinner filet has been, um, "bottom feeding". Fish that live in stagnant fresh water often develop off flavors due to algae. To avoid such problems, the fish can be kept in flowing water and fed a diet of corn and soy; this allows the fish to become virtually tasteless and thus commercially viable. (It should be noted that such a feeding regimen also alters the nutritional content of the fish.)
The Peace Corps saw tilapia as a source of inexpensive (or even profitable) protein for people who otherwise had few options; the fish could be farmed anywhere, fed anything, and the mud from the ponds could fertilize crops. This drove its popularity in developing countries, but it did not become a world-wide food until the 1990s when the corn-soy diet was introduced. It is now one of the most widely farmed fish in the world. Tilapia has since become an invasive species in some areas, its adaptability allowing it to out-compete native fish.