WA/WB basically means that either you or villain have 2-3 outs, so you want one bet to go in on each street.
OLD school thread where I first learned it.
one beef I have with the way ppl talk about it now is that just flopping an A or K doesn't qualify...you also need to be able to put villain on a hand range that is roughly 50/50 against yours. there have been a couple of times I've seen the line advocated in micro, for example, it was actually way way more likely that hero was ahead, and his opponent could still hold draws.
It's also discussed on pgs. 133-135 of HPFAP, "Playing Good Hands When it is Three Bets Before the Flop"