Beadlocks are generally used on off-road or race vehicles that encounter extreme conditions.
They allow the tire to be "aired down" (used at very low tire pressures) to provide maximum traction over extremely rough terrain.
Beadlocks use a locking ring that bolts over the bead of the tire, securing the tire to the wheel, to ensure that the tire stays on the wheel (or that ground friction does not exceed wheel to tire friction) while the air pressure in the tire is at a minimum.
Bead locks are not DOT approved and are not recommended for on road use.