Squamata is from the Latin squamatus, meaning: scaly, or having scales. The Squamata is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With nearly 11,000 species, the Squamata is the second-largest order of living vertebrates, with the largest being the perciform or perch-like fish.

Members of the order are distinguished by their skins, which bear horny scales or shields, and all members must periodically engage in molting. They also possess movable quadrate bones, making possible movement of the upper jaw relative to the neurocranium, which is the upper and rear portion of the skull forming the protective case around the brain. This is particularly visible in snakes, which are able to open their mouths very wide to accommodate comparatively large prey.

Squamates are the most variably sized living reptiles, ranging from the very small dwarf gecko (Sphaerodactylus ariasae) at 0.63 inches to to the 21 foot long reticulated python (Malayopython reticulatus). Too, the now-extinct mosasaurs reached lengths over 46 feet in length.

Interestingly, among reptiles, the squamates are the most closely related reptile to the tuatara, the last surviving member of the once diverse Rhynchocephalia, with both groups being placed in the clade Lepidosauria.