Definition: All Terrain Armored Transports, or AT-ATs for short, They first appear in The Empire Strikes Back at the Battle of Hoth, where they are called simply "Imperial walkers." In the DVD commentary for The Empire Strikes Back, Lucas stated that the AT-ATs were inspired by the Martian tripods from The War of the Worlds by H.G. Wells. The walkers were animated using stop-motion, with movement based on that of elephants.

Star Wars media is inconsistent on whether AT-AT is pronounced like the word "at" twice, or as each individual letter ("A-T-A-T"). Both pronunciations may be acceptable in-universe.

In-universe: AT-ATs are about 50 feet tall and have the appearance of giant four-legged monsters. The head serves as the control center and a mount for the walker's weapons: a set of laser cannons and a secondary set of blasters. The head is mounted on a flexible neck to give it a wider range of fire.

AT-ATs' legs allow them to step over terrain that might be difficult to navigate in a wheeled or treaded vehicle. However, they also made AT-ATs slow, hard to maneuver, and vulnerable to tripping, as the Rebel pilots soon discovered at the Battle of Hoth. Once an AT-AT was on its knees, the relatively unarmored top was an easy target. Even with this vulnerability, however, AT-ATs served the Empire's purpose: to strike fear into the hearts of their enemies.