Offside is 10 yards from a lineout. For a ruck the offside line for each team is thee hindmost foot of their last player in the ruck. For a scrum the offside line is again the hindmost foot except for the scrum half for whom the offside line is a line through the ball.
A player is also offside if he is in front of a player from his own team who last played the ball.
Ah yes. That's all very well. But, whats the difference between a Ruck and a Maul?