What are the rules for long jump?

Answer 1

A legal jump is one that counts, i.e. the jump is measured and goes towards the athlete's result.

An "illegal" jump would be one where a foul is committed. This includes, taking off in front of the take-off board, landing outside the pit, walking out of the front of the pit or taking longer than the allotted time.

Answer 2

When you either step past where your not supposed to or you don't jump close enough to the board

Answer 3

It is a foul which does not get measured. Typically because the athlete has taken-off beyond the take-off board.