a part in a song of any genre where the music is played usually in slower time or tempo and is slower and more rhythmic and will usually repeat oa number of riffs. has nothing to do with guitars, vocals or any other instrument other than drums. all the bullshit you see about its being a "brutal part of a hxc/metal song where people hxc dance" is 100% bull shit. most breakdowns have no relativity to brutalness.
The breakdown at the end of "Streetcar" by Funeral for a Friend is a prime example of a breakdown.