On a passing play, the quarterback takes the snap from his center and drops back to a passing position.
Typically a drop back consists of a three-step, five-step, or seven-step drop. The shorter the drop back, the quicker the quarterback gets rid of the ball. Examples where a quarterback uses a three-step drop include a quick slant or five-yard out pattern. Five- and seven-step drop plays might be a screen pass or a post pattern.