Define pawn break...

I was reading a book that kept talking about pawn breaks.  I get the general idea of what a pawn break is, but I haven't been able to really define what it is.  Anyone want to take a shot?

I'll make an attempt: It's a maneuver where a flank pawn moves to attack a center pawn which is blocked from advancing. Its goals are usually to open lines, control the center, and gain space, and also to trade the flank pawn for the more valuable center pawn.

A pawn advance which puts it in conflict with another pawn.

This is the position after 1. e4 e6 2. d4 d5 3. e5 (French defense, advance variation). Black to move has two pawn breaks to challenge White's centre - the first is c7-c5, the second is f7-f6. White's pawn break would be to play pawn from f4-f5 (after a preparatory f2-f4 :P) Technically I suppose you could call White's c2-c4 a pawn break too, but that would not be all that advisable me thinks :P

Actually, I wouldn't advise the f7-f6 pawn break for Black for the same reason the c2-c4 pawn break is inadvisable for White: it creates a backward pawn on e6 and a weak square directly in front of it.

You generally play f6 in the French advanced after you put as much pressure on d4 as you can. If you don't play f6 you'll just be slowly crushed, so while you may not recommend it, I would say it's borderline necessary.

Is a pawn break the same as a pawn lever?

yes it is although pawn break is a more commonly used

http://www.chesscafe.com/text/heisman17.pdf