A modern urban "tactic" employed in firearms training to get around obstacles while continuing a forward movement. It is most often employed by Airsoft or Paintball gamers, however it may be used by live-fire weapons personnel as well.
The technique, almost always done while running, involves diving forward in such a way that your shoulder lands on the ground first, and you roll into a little ball. As you come out of the ball, immediately spring back up into a running stance, or move into a kneeling position.
A Tuck and Roll can be seen in the movie "SWAT" during the shooting range sequence.