What does the term "mark it" mean in AFL?

Question

What does the term "mark it" mean in AFL?

Answer 1

A mark in AFL is where the ball has been kicked and caught without the ball being touched by another player or the ground in flight, also the ball has to have travelled a minimum of 10 meters in flight. This entitles the catcher a free kick. A player from the opposite side has the option of standing where the ball has been caught to prevent the catcher from running on with the ball. This spot where the ball was caught is also a mark.

Answer 2

See above, but current rules in AFL (as opposed to VFL, SANFL etc) require that the ball travels 15 meters before being caught, not 10.