This is an alphabetical list of selected unofficial and specialized terms, phrases, and other jargon used in baseball, along with their definitions, including illustrative examples for many entries.

The number 1 in baseball refers to the pitcher's position, a shorthand call for throwing to first, a single hit, and a fastball sign.

Catcher (2) gets a "Two!" call for throws to second, a "two-bagger" is a double, and the number 2 signs for a curveball.

The first baseman (3) receives throws with shouts of "Three!", nabs runners attempting triples ("three-baggers"), and the number 3 might signal a slider from the pitcher.

A process that allows a player to be removed from his team's 40-man roster.

Referring to a fastball. "He dialed up that pitch."

'Roll a bump' is a colloquial east coast slang for turning a 1-6-3 double play or a 1-4-3 double play.

The World Series—the championship series of Major League Baseball, in which the champion of the American League faces off against the champion of the National League. Typically, this series takes place in October, so playing in October is the goal of any major league team. Reggie Jackson's moniker "Mr. October" indicates that he played with great distinction in the World Series for the Yankees. Another Yankee, Derek Jeter, picked up the nickname "Mr. November" after he hit a walk-off home run in Game 4 of the 2001 World Series just after midnight local time on November 1. By comparison, Yankees owner George Steinbrenner's dubbing another of his players (Dave Winfield) "Mr. May" expressed his disappointment with that player's performance in the Fall Classic.