What does “retina display” mean?

My current iPad2 is cracked (taped together after I dropped it but I can still see the screen) and now, months after dropping it, the button to change screens does not work (it takes about 10 tries before I can get it to work.)  This button problem is a bigger problem — and it is very annoying.

The new iPad3 is supposed to be out soon with “retina display” and I don’t know what that is and whether I should wait for iPad3.

So…what is “retina display?” and should I wait?