Taking a mark happens when a player catches the ball in a defensive position.
It was introduced to give protection to full-backs and other players trying to catch high up-and-under kicks in pressure situations.
Calling a mark is a great way of relieving the pressure in defence when the opposition are on the attack inside the 22-metre line.
A player can only make the mark when they catch a high ball inside their own 22-metre or in-goal area.
As they catch the ball they shout "MARK".
If they catch the ball cleanly, the referee will give that player a free-kick on the spot where they caught the ball.
Only the player who has called for the mark can take the kick.
They then have the chance to clear their lines.
One thing to note is that a mark cannot be called when a player catches the ball direct from the kick-off.