Dead Ball – the time after an official designates a play to be over and before another play begins
 
Defense – the team without possession of the ball, in charge of keeping the “Offense” from taking the ball into the “End Zone”

Defensive Back – the defender usually in charge of covering receivers – “Corner Backs,” “Safeties” 

Defensive Backfield – the area behind the “Defensive Line” where the “Defensive Backs” generally line up

Defensive End – a defender who lines up at the end of the “Defensive Line,” usually in charge of containment on running plays and rushing the “Quarterback” on pass plays

Defensive Holding – using the hands to hinder a receiver by holding or pushing him back from catching a pass more than five yards away from the line of scrimmage

Defensive Line – usually the largest defenders on a team, DLs line up across from the “Offensive Line”

Defensive Lineman – the players on the “Defensive Line”

Defensive Tackle – a defender who lines up on the interior of the “Defensive Line”

Defensive Team – See “Defense”

Delay of Game – allowing the “Play Clock” to drop to zero before calling a play and snapping the ball, having more players than allowed on the field, or calling a “Time-Out” when none remain; results in a 5 yard penalty

Dime Back – a sixth “Defensive Back” brought in for “Dime Coverage”

Dime Coverage – a defensive strategy employing six “Defensive Backs,” as opposed to the usual four, generally only used in long passing situations 

Dime Package – See “Dime Coverage”

Division – a conference sub division; the NFL has four divisions per “Conference”

Double Coverage – two defenders covering the same receiver, usually only utilized for the best receivers, as this takes a “Defensive Back” away from his usual coverage responsibilities

Double Foul – when both teams commit a penalized offense during the same play, usually negates the need for penalty enforcement

Double Team – See “Double Coverage”

Down – an entire play from the time the ball is snapped until the officials rule it a “Dead Ball;” the offense gets four downs to move the ball 10 yards at a time

Down and In – A “Pass Pattern” in which the receiver runs down field and “Cuts” toward the center of the field

Down and Out -- A “Pass Pattern” in which the receiver runs down field and “Cuts” out toward the sidelines

Down Box – A sign carried by an assistant official keeping count of the “Down”

Down Lineman – a “Defensive Lineman”

Draft – the process of selecting players from college for the NFL

Draft Choice – a player selected by a team in the NFL Draft

Draw – a deceptive play designed to look like a pass, but when the quarterback drops back he “Hands off” to a “Running Back” --  usually called to counteract an overly aggressive pass rushing defense

Drive – a collective term for the series of downs from the time a team has possession of the ball until they either score or turn possession over to the other team

Drop Back – when a “Quarterback” steps backward after taking the “Snap” in preparation to attempt a “Pass”

Drop Kick – an extremely rare play in the NFL in which a player drops the ball and attempts to kick it through the “Uprights”; worth two points