A peacoat is a heavy wool jacket with buttons down the front. Peacoats were originally worn by European navy sailors, but now they're worn by hipsters.
Today peacoats are common — they're the hip-length, double-breasted, navy blue jackets you see all varieties of people wearing. Once they were worn exclusively by sailors in the navy, and called "pea jackets." The origin of the name peacoat is uncertain, but experts think it either comes from the Dutch pijjekker, "jacket of coarse woolen cloth," or from pilot cloth or P-cloth, a waterproof material used in the US Navy.