OFFSIDE.

       
Definition;When a player is nearest to his opponent's goal line rather than the ball and the second last defender.
A player is being penalised in offside by doing the following;

 1.Interfeering with play.
 2.Interfeering with an opponent.
 3.Gaining advantage by being in that position.

NOT OFFSIDE;
 1.Level with the second last defender.
 2.Touches the ball from the centre line.
 3.Goal kick
 4.Throw in

RECEIVING THE BALL FROM OFFSIDE POSITION IS TOTALLY NOT ALLOWED.