Its when your internet goes out and you need to rely on the porn and pirated movies you have downloaded. If you don't have any downloaded then you are pretty much dead.
It's behind the second-last defender. The last defender is, usually, the goalie but it really doesn't matter for the call. You can also not be off-side in your own half, or after directly receiving the ball after a throw-in, goal kick or corner kick or if the ball originated from either an opposing player or from a team mate that would already be considered off-side should they receive a ball (as in your teammate defeated the defenders in regular play with the ball). Furthermore, off-side is never applied to any backward pass, it must be from a pass toward the enemy goal.