A chair is a piece of furniture designed to provide seating for one person. It typically consists of a flat surface to sit on (the seat), a backrest for support, and often four legs for stability. Some chairs also include armrests, padding, or upholstery for added comfort. An office chair is a swivel chair with wheels and adjustable height, designed for use at a desk. It usually includes ergonomic features like lumbar support, armrests, and a cushioned seat to provide comfort during long periods of sitting. A dining chair is typically a stationary chair with a straight back, designed to be used at a dining table. It often has a wooden or upholstered seat, and may or may not include armrests, depending on the style.