I never really heard the term WBTB until recently, but it is a method I've employed for years. My understanding of it is very simple. If you are awake for a short period of time in the morning (like being woken by an alarm clock but then shutting it off and going back to sleep) when you fall back asleep you should enter pretty much immediatley back into dream mode. Rather than taking the long time it normally takes for you to enter a dream from when you first go to bed (the initial stages of sleep do not include dreams), it should be much easier to recognize a dream for what it is after just being conscious moments ago.
I have never heard or read anyone else's definition of WBTB, but this is how I understand it.