Parka, trench, bomber and pea are all types of coats, or outer garments worn over clothing for warmth and protection.
The names reflect different designs and origins. A parka is a hooded coat associated with Arctic peoples and cold-weather expeditions. A trench coat developed from military raincoats used during World War I. Bomber jackets originated as short flight jackets for military pilots, while pea coats became associated with sailors and naval uniforms.
A common mix-up is treating “jacket” and “coat” as completely separate categories. In everyday usage, jackets are usually shorter and lighter, but the boundary is flexible; a bomber is often called a jacket, while a pea coat is generally called a coat. All four are recognized forms of outerwear, with different materials, lengths and intended climates.