A splitter in baseball is a type of breaking pitch that looks like a fastball, but is slightly slower (usually between 80-90 MPH) and breaks downward suddenly before reaching home plate. It is designed to deceive batters into swinging off-time.
A much more common derivative of the forkball is the splitter. They are slightly slower than a fastball, usually between 80-90 MPH, and they break downward suddenly before reaching home plate. However, their break is not as extreme or sudden as a forkball, making them easier to throw and less susceptible to causing injury.