In baseball, the count refers to the number of balls and strikes a batsman has in his current plate appearance. It is usually announced as a pair of numbers, for instance "Three and One", with the first number being the number of balls and the second being the number of strikes. A 3-2 count—that is, one with the maximum number of balls and strikes—is referred to as a full count. A count of 1-1 or 2-2 is called even. Zero is always pronounced "oh".
The home plate umpire will signal the count with the number of balls on his left hand, and the number of strikes on his right hand. (As a result, it reads backwards when viewed from the pitcher's point of view.) Individual umpires vary in how often they give this signal; often it is done as a reminder when there has been a slight delay between pitches (such as the batter stepping out of the batter's box). It can also be a signal to the scoreboard operator that an incorrect count is being shown on the board. Some umpires may also give the count verbally, although usually only the batter and the catcher can hear it.
An important part of baseball statistics is measuring which counts are most likely to produce favorable outcomes for the pitcher or the hitter. Counts of 3-1 and 2-0 are considered hitters' counts, because the pitcher is more likely to throw a ball in the strike zone, particularly a fastball. Somewhat surprisingly, in general, a 3-0 count tends to yield fewer hittable pitches, depending on the situation (baseball fans have often suggested that this is because umpires are reluctant to call four straight balls and as a result 'ease up' on the fourth pitch, treating it as having a wider strike zone). Often batters will take (not swing at) a 3-0 pitch, since the pitcher has missed the strike zone three straight times already, and a fourth would earn the batter a walk. Counts with two strikes (except 3-2) are considered pitchers' counts. An 0-2 count is very favorable to a pitcher. In these counts the pitcher has the freedom to throw one (or sometimes two) pitches out of the strike zone intentionally, in an attempt to get the batter to chase the pitch (swing at it), and potentially strike out.
Arguing as to whether a pitch was a ball or a strike (which is a judgment call by the umpire) is strictly prohibited by Major League Baseball rules, and will quickly lead to a warning from the umpire. The player or manager may be ejected from the game if they continue to argue.