What is the strip on the pitcher's mound where a pitcher must stand called?

The strip on the pitcher's mound where a pitcher must stand is called the pitcher's rubber.

The pitcher's rubber is the white rectangular slab formally known as the pitcher's plate. A pitcher uses it as the reference point and push-off surface when delivering a pitch. In everyday baseball language, players and commentators often shorten the name to “the rubber.”

In Major League Baseball, the slab is 24 inches wide and 6 inches deep. Its front edge is exactly 60 feet 6 inches from the rear point of home plate, the regulation pitching distance. It sits on the raised pitcher's mound, which is a larger earth-covered area rather than the strip itself.

The rubber is sometimes confused with the mound. The mound is the entire elevated section, while the rubber is the narrow slab at its center. Its position also matters under the rules: when a pitcher is engaged with the rubber, actions such as stepping off, attempting a pickoff, or beginning a delivery are governed by pitching and balk rules. The distance was established in 1893.