terminology

I've been reading bits and pieces on various TT sites over the last couple of years and often find myself not being totally sure I understand some of the terminology. Some are obvious and I think I get most of the meanings but then I read a review on something and I'm not too sure. So could...

1. What is bottoming out? For the longest time I thought it was when I made a stroke and the ball never dug far enough into the rubber to make contact with the wood, and thus the ball would just drop as it was never propelled. But recently someone told me it happens more with thinner rubbers...