A trench coat is a specific kind of rain coat, which has a belt and is often double-breasted and buttons down the front. Movie spies and detectives are commonly shown wearing trench coats.
The classic version of a trench coat is made from waterproof beige cotton, belted, and extends below the knee. Trench coats were developed during World War I as a lighter alternative to the heavy serge coats typically worn by soldiers. The shoulder straps that many trench coats have were used to attach military rank insignia, and the name trench coat implied that officers wore them in the trenches during wartime.