A 20-inch bicycle typically refers to the size of the wheels, which are designed for children or smaller adults. These bikes are often used for recreational riding, learning to ride, or for short commutes. The smaller wheel size makes them easier to handle and maneuver, making them a popular choice for younger riders. Many 20-inch bicycles come with features like adjustable seats and lightweight frames to accommodate growing children. They can be found in various styles, including mountain bikes, BMX bikes, and cruisers, allowing riders to choose a design that suits their preferences and riding needs.