In baseball, a slider is a pitch halfway between a curveball and a fastball. When pitched, the slider breaks laterally and down, with more speed than a curve ball but less speed than a fastball. The break on the pitch is shorter than that of a curveball. The release technique of a slider is between a curve ball and a fastball. The slider is similar to the cutter, a pitch which is thrown as a fastball, but differs in the sense that a slider tends to be more of a breaking ball.
The innovator of the slider is debated, but some source Charles Albert Bender as the first to use the slider, then called a "nickel curve" in the 1910's. Bender used his slider to help him achieve a no-hitter and win 212 games in his career. Bender was the first pitcher to win six World Series.