A type of receiver in football that lines up the farthest from the center near the out of bounds line and is eligible to receive the ball. This type of receiver is also known as a "wide receiver".
An X receiver will be lined up on the line of scrimmage. The X receiver will be positioned on the opposite side of the field from the tight end (Y receiver). Because the X receiver is lined up wide to one side of the field, he is at times referred to as a "wide receiver", and because he is not lined up tight with the tackle but split off to the side, the X receiver is also at times referred to as a "split end".
He is sent far out into the far side of the field for several reasons. First, the opposing team must watch a wider part of the field. Second, from there the X receiver can throw a block and open up more of the field for the longer running back.