Domain flipping is finding a good high quality domain and regristering it, then onselling it. Say for example you purchase coins. com. This is going to appear (with a bit of seo) first on google under the search term coins so it is worth a lot more than the $9 paid to regrister.
Web site flipping, is registering a domain name, and getting to sell it after improving its stats, a lot of factors might go into how much you eventually sell it for, depending on for example age, if it's an EMD (Exact Match Domain), PR (Page Rank), Alexa Ranking e.t.c
Website flipping is one of the regular activity as people are selling shares. I think It will become regular practice in future.