A suit and a tuxedo are both formal wear, but there is a distinct difference between the two. A suit is a matching set of jacket and trousers made from the same fabric, with a shirt and tie. Suits are usually made from wool, and come in a variety of colors, including black, navy, and gray. Suits are usually worn to business meetings, weddings, and other formal occasions.
A tuxedo is a more formal version of a suit. It typically consists of a black jacket with a white shirt, a black bow tie, and black trousers with a satin stripe down each side. Tuxedos are usually worn to formal events such as black tie weddings, galas, and other very formal occasions.