Plain English Meaning

Ice forms inside a spark plug and connects the two metal points where the spark is supposed to jump. Instead of making a spark, the electricity takes the easy path through the ice, so the cylinder doesn't fire.

Full Definition

A condition in which ice accumulates between the electrodes of an older-style spark plug, forming a conductive path that shorts out the spark and prevents ignition of the fuel-air mixture in that cylinder. It typically occurs in cold, moist conditions when moisture condenses inside the spark plug and freezes across the gap.

Context Anchor

Seen in powerplant and carburetor icing discussions, especially when troubleshooting loss of engine power in cold or humid conditions.