glazing the bore happens when engine rpm remains constant for long periods of time, idling for example...
what happens is that the cylinder bore will wear out or get polished(hence the term glazed) between the distance the piston is travelling for long periods at a rev range up and down the bore. Due to the wear by glazing, above and below this distance the bore will be smaller making a shoulder, and when revs increase, the piston travel will also increase, the shoulder on the bore will destroy the piston rings prematurely...
this is especially common when running in re-co engines ...thats why you shouldnt drive at constant speed/rev with a reco engine until you have done a few hundred k's...and never idle for long periods....