The shadowing or darkening of an obvious light source, causing a dingy area... in most cases nauseating to behold.
For example, the layered car wreckage on the loading screen of Burnout Revenge, causes a shamhole when the car's drop shadow slides in front of a brilliant exploding fireball.
Dude, how dare you use a shamhole!
You're shamholing my style.
Popen my shopen... and while you're at it, jamhole my shamhole.