Kiethf,
Flipping is when you buy off-plan, paying only a deposit, and then sell on at a profit before the development is complete, thus also avoiding some of the taxes payable (I think) and also avoiding laying out the full cost of the property.
At the height of the property boom on the C de S some properties were flipped a number of times, each vendor taking a profit, before the developments were finally completed.
This only appears to work when there is a so called boom.
Hope this helps, though I'm sure some of the more knowledgeable members will have other ideas about flipping.