Flipping websites means selling a complete website to someone else, that would include the domain name, the hosting space and the website's content its self. Of course to do that you need first to have your own already made website published online.

 If you have a website that is well made and you no longer want to maintain it or whatever the reason you don't want to keep your website anymore, you can simply list it for sale instead of losing it completely. Buyers usually visit these listed websites, and check their statistics which include the rank, the traffic and the age of these websites.

 Those buyers usually have experience and good plans in dealing with old websites, they can just rebuild it or improve it which is a lot easier for them to than starting a website from the very beginning. The price of a website depends on many factors like the website's design, age, traffic, rank and income if it generates any.

One of the most famous marketplaces for buying and selling websites is "Flippa.com", once you join it you will be able to list your website for sale there, you can also browse the other listed websites and get an idea about how all this thing works.