The tall hat with a wide brim — the wide flat edge that goes all the way around — that cowboys wear in American films. Usually felt, usually with a dent down the top and a pinch at the front, and the brim often curls up a little at the sides. Strictly speaking, Stetson is a company: John B. Stetson started making these hats in America in 1865, and his hats were so much the standard that people began calling any hat of that shape a Stetson, whoever actually made it. That is why you often see it with a capital S, and why some careful writers will only use it for the real brand. In everyday speech nobody is that careful. It is the same move as calling every tissue a Kleenex. You will also hear 'cowboy hat' or 'ten-gallon hat' for the same thing, and 'cowboy hat' is the safer everyday word — 'Stetson' sounds slightly older, or slightly like you know about hats. It belongs to the American West and to country music; an English farmer in a wide hat would not be described as wearing a Stetson.