Tread

The tread of a tire or track refers to the rubber on its circumference that makes contact with the road or the ground. As tires are used, the tread is worn off, limiting its effectiveness in providing traction. A worn tire can often be retreaded.

The grooves in the tire are correctly called the tread pattern, or simply the pattern, but the word tread is often used casually to refer to the pattern of grooves molded into the rubber. The grooves are not the tread, as they do not make contact with the ground. This distinction becomes significant in the case of racing slicks: which certainly have a tread but do not have grooves, and so they neither have a pattern.