A jacket is a garment for the upper body, usually extending below the hips. A jacket typically has sleeves and fastens in the front or slightly on the side. A jacket is generally lighter, tighter-fitting, and less insulating than a coat, which is outerwear.
Trousers, slacks, or pants are an item of clothing worn from the waist to anywhere between the knees and the ankles, covering both legs separately. In the United Kingdom, the word pants generally means underwear and not trousers.