Loose scrum--this forms wherever the ball is lying free and players start scrapping for it. The ball must be played with the feet until it is kicked free.
Touch--this sensuous term simply means out of bounds. The ball must then be thrown in by the side which did not put it in touch. It must be passed in through a "lineout" formation in which the teams line up parallel to each other, and then jump for the ball, trying to kick it to their team-mates.
Knock-on--this phrase is used to describe any situation in which the ball is passed forward and which is almost always illegal, meriting a penalty.