A radial tire is a kind of tire that has plies or cords which run at right angles to the bead and parallel to the radius. This is a would be a very weak form of tire with a small bias angle. But radial tires have a very large bias angle. This makes for a very stiff tread area and a flexible sidewall. Allowing them to act independently.
An R on the side of a tire indicates that it is a radial, (as is P205/70R14). Most modern tires are of this form of construction.