Any variation of car(s), generally two or more, that all move the same damn speed in multiple lanes. Most often one of the drivers of a blockade vehicle is not paying attention and is in the passing lane, thus making it impossible for other cars to pass.
Drivers of said blockades are oblivious to honking/tailgating/light flashing. They have a sixth sense that keeps them at the exact speed of the car(s) next to them regardless of whether the other car attempts to speed up or slow down.
More often than not, annoyed drivers behind you will ride your ass thinking it will magically lift the blockade making for a most unpleasant experience.
Jeremy: dude whatthefuck you driving so slow for? i gotta drop a dookie
Thaddeous: SHUT THE FUCK UP! These commie shitfucks set up a mobile blockade the middle the damn highway. cant drive any faster.