The best way I have heard end grain described is that it is to picture a hair brush. If you put your knife down into the bristles then the bristles kind of separate and surround the blade. This is what end grain wood does. You slice down into the grain and that is much more gentle on your blade than anything else.
There are end grain boards and edge grain boards. End grain are the better (and more expensive) of the two and are the ones I was using the brush to help describe. Edge grain are like end grain turned on their side.