People use the term "flip" very loosely. It can refer to flipping a contract, or flipping a property by buying and immediately reselling, or buying, rehabbing, and reselling. No one has ever given me an accurate legal definition, and most people just use it as short for buying and reselling relatively quickly.
_________________________
There is no "legal" definition. I have flippers that get the property under contract and have it sold prior to close and double close it (wholesale). Other clients will buy it, put in repairs and resale it quickly. Others will buy it, do extensive rehab work and resale it quickly. To me they are all Flippers.
To me the term is generic meaning we want to make alot of money in a short amount of time, with minimal exposure. I always ask the potential client what they mean by "flipping".