The red-eared slider or red-eared terrapin is a subspecies of the pond slider, a semiaquatic turtle belonging to the family Emydidae. It is the most popular pet turtle in the United States, is also popular as a pet across the rest of the world, and is the most invasive turtle. It is the most commonly traded turtle in the world.

The pond slider is a species of common, medium-sized, semiaquatic turtle. Three subspecies are described, the most recognizable of which is the red-eared slider, which is popular in the pet trade and has been introduced to other parts of the world by people releasing it to the wild. Hatchling and juvenile pond sliders have a green upper shell (carapace), yellow bottom shell (plastron), and green and yellow stripes and markings on their skin. These patterns and colors in the skin and shell fade with age until the carapace is a muted olive green to brown and the plastron is a dull yellow or darker. Some sliders become almost black with few visible markings. The carapace is oval with a bit of rounding and a central crest with knobs, but these features soften and fade with age, adults being smoother and flatter. For determining an adult slider's sex, males typically have much longer front claws than adult females, while females usually have shorter, more slender tails than males. Their lifespans range from 20 to 50 years.