n. The dirt, dust, and other grime that accumulates on computer keyboards.
1998
Some of CompuClean's customers even turn to them for other services above and beyond the level of keyboard plaque, even though cleaning remains the primary service.
1995 (earliest)
Keyboard Plaque: The disgusting buildup of dirt and crud found on computer keyboards. "Are there any other terminals I can use? This one has a bad case of keyboard plaque."