A tricycle is a small land vehicle, human powered, similar to a bicycle, but with three wheels. Tricycle is commonly shortened to trike.
These wheels can be arranged either with one steering in front and two parallel behind (delta), or with two steering in front and one behind (tadpole).
In the case of delta tricycles, the drive is often to just one of the rear wheels, though in some cases both wheels are driven through a differential. Most tadpole trikes drive their single rear wheel.
Many small tricycles are designed for use by small children. They are considered to be easier to learn to ride due to not requiring the ability to balance a bike. Adult tricycles are much less popular than bicycles, and adults often find tricycles to be very difficult to ride even in a straight line on level ground due to their familiarity with the counter-steering required to balance a bicycle.
Some designs of tricycle are particularly well suited for load carrying, others are designed for racing or for comfort. Recumbent tricycles are probably more popular now than upright tricycles. Some forms of these are fully enclosed and intended for all weather use. These are known as velomobiles.
In the UK, upright tricycles are sometimes referred to as "barrows".
Links to discussions and manufacturers of adult tricycles:
Also see bicycle, velotaxi, velomobile
