Fastballs are (obviously) the hardest, straightest pitch, and any movement tends to be "tailing", meaning a right-handed pitcher's FB will tend to break slightly to the right at the end of the trajectory. A cutter is a pitch that is designed to counteract this tail. If a right-handed pitcher throws a fastball to a left-handed hitter, the tailing action could leave the ball over the plate. A cutter is thrown so the ball continues to ride in towards an opposite-handed hitter. Mariano Rivera probably has the best cutter in baseball right now. A change up is designed to use the same arm motion/speed as a fastball, but be slower, thus fooling the hitter into swinging early. The ball is either palmed or somehow "choked" in the hand to slow the motion. Changeups have a natural downward break due to the slower speed. The Curve is a slow pitch (usually in the 65-75 mph range) that breaks straight down, or "11 to 5" in clock terms. A Slider is thrown harder than a Curve (usually in the 75-89 mph range) that has more of a "10 to 4" break to it. It's designed to look like a fastball out of the hand but breaks out of the zone Sinkers/Forkballs/Splitters are grip variations on the same pitch, which is thrown hard like a fastball, but has late downward break to it. Unlike the slow curveball, the sinker is generally thrown in the mid to high 80's. As for "backdoor" pitches, these are references to how the pitch breaks compared to which side of the plate the hitter is on. For example, a backdoor slider is when a right-handed pitcher throws a slider to a left-handed pitcher and the pitch breaks from outside the zone over the plate. Technically, you can throw a "front door" slider, where a right handed pitcher throws to a right-handed batter and the pitch breaks from inside the plate back over the zone.