the practice of preventing another driver from changing lanes. specifically, when a driver wants to change lanes while through-travelling, but finds himself stuck behind slower traffic, he may wish to pass the other vehicle. a lane blocker, however, will find a way to keep the passing driver stuck in postition, making it impossible for the passing driver to get around safely. usually this is a passive action, as opposed to on-ramp blocking or offramp blocking; often the offending driver is unaware of the faster car wanting to go past (often because the offender is talking on a cell phone.)
eric: come on man, just pass this truck! we're going to be late for the concert!
derrick: i can't pass him! the damned avalon in front of us is lane blocking me!
eric: flash your high-beams to get his attention!
derrick: i tried, but he's talking on his cell phone! must be more important than driving safely.
eric: what a dumbass bastard}!