From the eWrestling Encyclopedia.

Neckbreaker slam

Also known as a Falling neckbreaker. This move sees the attacking wrestler stands back to back with their opponent, then reaches over their shoulder and seizes the opponent by the back of their neck or head. The wrestler then falls to their back while maintaining the hold, dragging the opponent down with them to drive their back into the ground. This move is often used by a wrestler who ducks under an attempted attack by the opponent, e.g. a clothesline, and is thus back to back with their opponent.

A slight, but common, variation of this, also known as a Jumping neckbreaker, sees the attacking wrestler jump up after seizing the opponent's head so that they fall to the mat from a greater elevation and with more force. Mickie James uses a variation of this in which she first traps the arms of her opponent, and then hits the slam. Mike Mizanin also has used this move as his finisher which is usually preceded by a Running knee lift he would then slam his opponent to the ground. he calls this variation the Reality Check.