A retread, or "recap," is a previously worn tire which has gone through a remanufacturing process designed to extend its useful service life.
Retreading starts with a safety inspection of the tire. The old tread is then buffed away, and a new rubber tread is applied to the bare "casing" using specialized machinery.
Retreads are significantly cheaper than new tires. As a result, they are widely used in large-scale operations such as trucking, busing and commercial aviation. They are also the most environmentally friendly way of recycling used tires - in some applications, a tire can be retreaded up to 10 times. Recycled rubber from retreads can be shredded to make rubber mulch. The process of "retreading" requires, after the buffing off of the old tread, there to be coating with another compound like rubber to allow the new tread to adhere to the used tire casing.
During World War II, the term "retread" was used to describe Army officers who had left the service before the war began for any reason (failure of promotion, medical disqualification, reduction in force, retirement, etc.), but who had been recalled to active duty in the Army Reserve for the duration of the war.