Spun bearings... on the connecting rod, the bearings between the connecting rod and the crank have oil holes that line up with the connecting rod. If the bearing spins around where this is no longer lined up, then you have a spun bearing.
To throw a rod is exactly that. When an engine has bad rod bearings, poor lubrication and such, you'll normally hear a heavy deep tone knock each time the piston moves up and down. During running, the bearing end cap may finally give up, break loose, and the piston can litterly blow right through the side of the motor/oil pan., leaving a great big mess on the ground. Other things that can cause this is the connecting rod itself can stress out and actually break in half. Either way you look at it, not a good thing.
