On-deck
In baseball, on-deck refers to being next in line to bat. In a professional game, the batter who is on deck traditionally waits in a location in the foul territory called the on-deck circle.
Being on-deck only guarantees the batter will get a chance to bat in the inning if there are fewer than two outs, and the number of outs plus the number of baserunners adds up to fewer than three, because a double play or triple play could occur. Additionally, the manager reserves the right to pull the on-deck hitter for a substitute at his discretion.
The player next in line to bat following the on-deck batter is colloquially referred to as being in-the-hole.
On-deck circles
There are two on-deck circles in the field, one for each team, positioned in foul ground between home plate and the respective teams' benches. The on-deck circle is where the next scheduled batter, or "on-deck" batter, warms up while waiting for the current batter to finish his turn. The on-deck circle is either an area composed of bare dirt; a plain circle painted onto artificial turf; or often, especially at the professional level, made from artificial material, with a team or league logo painted onto it.According to Major League Baseball rules and NCAA baseball rules, there are two on-deck circles. Each circle is in diameter, and the centers of the circles are apart. A straight line drawn between the centers of the two on-deck circles should pass behind home plate. In the Official Baseball Rules published by Major League Baseball, the on-deck circle is referred to as the "next batter's box".