A strategy in which a player on the offensive team will make contact with a defensive player in an offer to direct them in a particular direction that gives an advantage to the offensive play. This usually falls under one of two categories: run blocking, where the team will attempt to open lanes for a ball carrier to gain yards, and pass blocking, where the team will attempt to keep the defense from reaching the quarterback to allow him to complete a pass downfield. Blocks are only legal if the person does not significantly grab onto the opposing player, if so it is a penalty.
A block is a catch-all term for any time that an offensive player makes contact with a defensive player to put them in them at a disadvantage. The most common blockers are the offensive linemen. These players block on every down, although the particular location and strategy of blocking changes from play to play. Other players can block on given plays depending on the play call. For instance, on pass plays a tight end or running back might be kept in to help pass block in addition to the offensive line.