Balk: An illegal, often deceptive move by the pitcher, penalised by a ball being called, or letting baserunners advance one base.

   Ball: A pitch outside the strike zone that the batter does not try to hit.

   Base: One of the three safe stations for the batter or baserunner.

   Baseline: The direct line between each base, along which the baserunner must generally run.

   Baserunner: A batter who has reached base safely.

   Bases loaded: Bases are said to be loaded when there is a baserunner on each base.

   Batter: The player trying to hit the pitch.

   Batter's box: A rectangular area beside home plate where a batter stands to hit the pitch.

   Bullpen: The area where relief pitchers wait, or prepare, to enter the game.

   Bunt: An attempt by the batter to tap the ball instead of swinging at it.

   Catcher: The fielder positioned behind home plate who catches the pitches.

   Centerfielder: The fielder positioned in centre field (near the middle of the outfield).

   Changeup: A pitch thrown deceptively slowly to surprise the batter.

   Curveball: A pitch thrown with a rotation that makes the ball curve.

   Designated hitter: A player who bats in place of a designated team-mate (usually the pitcher) in the batting line-up.

   Double: A hit that allows a batter to reach second base.

   Double play: A play in which two outs are made with one pitch.

   Dugout: The semi-enclosed area beside the playing field where players sit when they are not actively involved in the game.

   Error: A mistake by a fielder that lets a batter or baserunner advance to a base.

   Fair ball: A ball hit into the field of play.

   Fastball: A pitcher's fastest pitch.

   First baseman: The fielder stationed near first base.

   Flyball: A ball hit in the air to the outfield.

   Forceout: An out made when a baserunner, forced to run because another team-mate must run to the base he is occupying, cannot make the next base safely.

   Foul ball: A ball hit outside the foul lines.

   Foul lines: The two straight lines, extending from home plate past the outside edges of first and third bases to the outfield fence, which define fair territory.

   Foul tip: A ball that barely touches the bat before continuing to the catcher.

   Grand slam: A home run with a baserunner on each base, scoring four runs.

   Groundball: A ball hit along the ground.

   Hit: A ball struck by a batter that enables him to reach base safely.

   Home plate: The five-sided slab of whitened rubber, 17 inches wide, which the batter stands beside to hit the pitch.

   Home run: A hit by a batter, which usually goes over the outfield fence, that enables him to run around all the bases safely.

   Infield: The diamond-shaped area formed by the three bases and home plate.

   Infielder: A fielder in any of the four infield positions, not including the pitcher and catcher.

   Inning: A turn at batting and fielding for each team.

   Leftfielder: The outfielder stationed in left field (the left-hand side of the outfield from the batter's perspective).

   Line drive: A ball hit sharply in a straight line roughly parallel to the ground.

   Live ball: A ball in play.

   Mound: The packed hill of dirt in the middle of the infield from which the pitcher throws the ball.

   On deck: Due to bat next.

   Outfield: The playing area inside the foul lines and beyond the infield.

   Outfielder: A fielder in any of the three outfield positions.

   Passed ball: A catcher's failed attempt to catch a good pitch, allowing a baserunner to advance to the next base.

   Pickoff: A play between pitches in which a fielder tags a baserunner out with the ball while he is standing off, or leading off, base.

   Pinch hitter: A player who bats in place of a team-mate one time in a game.

   Pinch runner: A player who replaces a baserunner on his team one time in a game.

   Pitcher: The player who throws the ball to the batter.

   Popup: A ball hit in the air to the infield.

   Relief pitcher: A pitcher substituted into the game.

   Rightfielder: The outfielder stationed in right field (the right side of the outfield from the batter's perspective).

   Rubber: The rubber slat on the mound, against which the pitcher must plant his back foot when pitching.

   Run: The point scored when a batter or baserunner advances to home plate.

   Run batted in: The credit a batter receives for a turn at bat that enables a team-mate to score a run.

   Sacrifice: A bunt that allows a baserunner to move to the next base while the batter gets out.

   Sacrifice fly: A flyball hit far enough to enable a baserunner on third base to score a run after the ball is caught.

   Scoring position: A good position for scoring a run on most hits, referring specifically to a baserunner standing on second or third base.

   Second baseman: The fielder stationed near second base.

   Shortstop: The fielder normally positioned between the second and third basemen.

   Single: A hit that allows a batter to reach first base.

   Sinker: A pitch thrown with a grip that makes it drop lower as it reaches home plate.

   Slide: A baserunning manoeuvre in which the player slides into a base so he does not have to slow down to avoid overrunning it, or to make it difficult for the fielder to tag him with the ball.

   Slider: A pitch essentially mixing a fastball and a curveball, thrown almost as hard as a fastball with a rotation that makes the ball curve more slightly than a curveball.

   Squeeze play: A play in which the batter bunts to try to let the baserunner on third base score a run.

   Starting pitcher: The pitcher for each team at the start of the game.

   Steal: A baserunner's successful advance from one base to the next on his own, usually during a pitch that is not hit.

   Strike: 1. A pitch judged by the umpire to have passed over home plate between the batter's armpits and the top of his knees. 2. A pitch that the batter fails to hit when he swings. 3. A foul ball when the batter has fewer than two strikes against him.

   Strike zone: The area over home plate between the batter's armpits and the top of his knees, where a pitch is called a strike even if he does not swing the bat.

   Strikeout: An out where the batter gets three strikes.

   Suicide squeeze play: A play in which the batter bunts to try to let the baserunner on third base score a run. The difference between this and a normal squeeze play is that baserunner starts running towards home plate as soon the pitch is thrown.

   Third baseman: The fielder stationed near third base.

   Triple: A hit that allows a batter to reach third base.

   Triple play: A play in which three outs are made with one pitch.

   Walk: An automatic advance to first base for the batter after the pitcher throws four balls.

   Wild pitch: A pitch thrown so wildly that the baserunner advances to the next base.

Credit: IOC

For further info., please visit http://www.olympic.org/uk/sports/programme/disciplines_uk.asp?DiscCode=BB.