Wiktionary
alt. A bodysuit-like undergarment that makes the wearer look fatter n. A bodysuit-like undergarment that makes the wearer look fatter
Wikipedia
A fatsuit is a bodysuit-like undergarment used to thicken the appearance of an actress or actor of light to medium build into a heavy-set or obese character, in conjunction with prosthetic makeup. Other spellings include fat suit and fat-suit. Fatsuits worn by characters are either deliberately visible or mainly concealed. Most are intended as unseen body padding beneath a costume (e.g., Rosemary Shanahan in Shallow Hal, and Sherman Klump in The Nutty Professor), others appear as realistic flesh and are viewed directly (e.g., Fat Bastard in Austin Powers, and Les Grossman's hands in Tropic Thunder). A fatsuit is often used to provide comedic effect, as in "Weird Al" Yankovic's music video, " Fat" and the video " Keine Lust" by the German band Rammstein.