Skipping vs. Drop Outs not "High School "

What is the difference??? Are drop outs mainly due to faltering CD player performance or disc problems? Some old and some brand new discs are having drop outs on them (which I've never heard before on my system), but not much skipping.

I am using a 1997(?) Marantz CD63 mkII -> AA DTI-Plus -> AMC DAC8. (in other words: old crap)

Thanks!!!

Brad
Atlanta