A post is a moderate to deep passing route

Route (football)

A route is a path or pattern that a receiver in American football runs to get open for a forward pass.-List of common routes:*Curl route*Drag route, also called an "In route"*Corner route, also called a "Flag route"...

 in American football

American football

American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football. The ball can be advanced by...

 in which a receiver

Wide receiver

A wide receiver is an offensive position in American and Canadian football, and is the key player in most of the passing plays. Only players in the backfield or the ends on the line are eligible to catch a forward pass. The two players who begin play at the ends of the offensive line are eligible...

 runs 10-20 yards from the line of scrimmage

Line of scrimmage

In American and Canadian football a line of scrimmage is an imaginary transverse line beyond which a team cannot cross until the next play has begun...

 straight down the field, then cuts toward the middle of the field (towards the facing goalposts, hence the name) at a 45-degree angle.

It is designed to stretch the opposing secondary deep down the field, opening holes in the coverage over the middle. It works particularly well against secondaries that don't have more than one safety who is effective in coverage. It tends to induce the opposing defense to play a deeper field and drop more defenders into deep coverage, but this may still open up the run. Cover 3 packages can be effective against it, if the defender in middle deep coverage is perceptive enough.

To run the route effectively, a wide receiver must be adept at catching the ball in traffic, and have the vertical ability and strength to rise above the top of a safety to catch the ball.

A variant of the post pattern, in which the receiver cuts infield at a shallower angle, is called a skinny post. It is designed to find a hole in deep coverage, cutting shallow inside the deep sideline defender, but not far enough to draw the middle defender.