Math Rock (from Wikipedia):
"Math rock is a rhythmically complex, guitar-based style of experimental rock that emerged in the late 1980s. It is characterized by complex, atypical rhythmic structures (including irregular stopping and starting), angular melodies, and dissonant chords."

here is a stupid(!) example: http://www.youtube.com/watch?v=RztR4E12dGU

here is a explanation: http://www.youtube.com/watch?v=MHDAn9Qgb9M