What does bored out 75 over mean?

The term "bored out" usually means that the cylinder has been bored to a new dimension. In this case it would mean that the 'original' dimension was 75mm. It has been rebored to a new dimension, whatever that is. Re-boring is necessary when increasing the diameter of the piston. It does require a automotive machinist to accomplish this job and to obtain the correct clearances. Dependent on the type of cylinder, it may require replating of the cylinder walls, ie: 'Nikasil'.