From ibikeu Wiki

The tire is the outer layer of rubber that is in contact with the ground. It is mounted on the rim of the wheel. Usually there is a separate tube inside the tire which contains pressurized air. The tire protects the lighter, more flexible tube from damage. Almost every tire has a size and suggested pressure imprinted on the sidewall.

There are two types of tire that do not use tubes: Tubeless and Tubular. Tubeless tires, currently available only for mountain bikes, allow extremely low pressures to be run without the risk of pinch flats. Tubular tires, for road bikes, have traditionally offered the lowest rolling resistance of any tire, as well as good traction for cornering. Standard tires have recently advanced to almost meet this standard.

Much could be said about the durometer of various tires, but in practice this is arguably mostly marketing.