The application of semi-algebraic principals towards a sound pattern for electronic music. "X" being the time slot in the pattern where a sound sample could/should be used. If applied correctly, an equation of sound samples equates from the overall pattern itself, thus creating the most intense pattern of sound possible, for that point in a track. It's the natural sense of rhythm.
Many drum & bass/idm/breakbeat/breakcore musicians use the subconscious algorithms of X of Sound.