Loricariidae is the largest family of catfish (order Siluriformes), with 92 genera and just over 680 species to date, with new species being described each year. Loricariids originate from freshwater habitats of Costa Rica, Panama, and tropical and subtropical South America. These fish are noted for the bony plates covering their bodies and their suckermouths. Several genera are sold as "plecos", notably the suckermouth catfish, Hypostomus plecostomus, and are popular as aquarium fish.
Members of the family Loricariidae are commonly referred to as suckermouth armoured catfishes, armoured catfish, 'plecos' or simply 'plecs'; a shortened form of the species name Hypostomus plecostomus. Some loricarids are not normally considered plecostomus, such as farlowella catfish.
These names are used practically interchangeably when referring to the Loricariidae. The name "Plecostomus" and its shortened forms have become synonymous with the Loricariidae in general, since Plecostomus plecostomus (now called Hypostomus plecostomus) was one of the first species imported for the fish-keeping hobby. This can cause some confusion, as some unrelated fish may also be called plecostomus, such as the "Borneo plecostomus", which is actually a balitorid fish.
In their native range, these fish are known as cascudos or acarís.
Some types of loricariids are often referred to by their 'L-number'; this has been become common since imports of loricariid catfish from South America often included specimens that had not been taxonomically described. Currently, L-numbers are used not only by fish-keeping enthusiasts, but also by biologists, since they represent a useful stopgap until a new species of fish is given a full taxonomic name. In some cases, two different L-numbered catfish have turned out to be different populations of the same species, while in other cases, multiple (but superficially similar) species have all been traded under a single L-number.