What is the meaning of Plate_appearance?

A batter's completed turn in the batter's box. It usually results in an at-bat or walk, but may also result in a hit-by-pitch, sacrifice fly, sacrifice hit, or catcher's interference. If the third out of an inning is recorded prior to completion of the batter's turn, no plate appearance is credited to the batter, and he will lead off his team's next turn at bat.

Source: wiktionary.org