A trailer bike (also known as a trailer cycle, and trademarked names such as Trailerbike, Trail-a-bike, Half wheeler or Tagalong) is a one-wheeled, or sometimes two-wheeled, bicycle trailer designed to carry one or more children in positions that closely resemble that of a bicycle rider. It can be described as the, "back half of a bicycle." The rider of a trailer bike usually has a saddle, handlebars, and pedals. Some fold for more compact storage.