excessive piston to bore clearance means that the gap (tollerance) between your piston and the sidewall of your cylinder/block is too large. usually will cause blow-by. the burning of oil, and dark exhaust smoke. also may cause the engine to have a weak compression stroke

If you have a bore scope that will fit in through the spark plug hole, you can look at the surface of the cylinder walls. If there are excessive marks on the sides, or the front and back, they must be pulled and repaired.

It is bore da, pronounced phonetically "bore-eh daah"
bore da

Rifled bore and Smooth bore

In Full bore ball valve, The bore dia will be same as internal dia of the pipe.In reduced bore, the bore dia is reduced than the ID of pipe.