The word flipping refers to "buying something for cheap and then selling it for a higher price." Therefore, domain flipping is buying domains for a cheap price and selling them later for a higher price. Likewise, website flipping is buying a website, or building a website, for a small price and then selling them for profits.
There are a lot of marketplaces where you can make money by domain flipping and website flipping. The most reputed domain and website marketplace is Flippa.
Do you actually make money by domain flipping and website flipping, what is the cost like? How much you can actually make?
In 2016, when Mark Zuckerberg's daughter was born, a guy from India registered a domain on Zuckerberg's daughter's name for less than $10. Facebook bought that domain for $700.
The key is registering the right domain name.
As far as website flipping is concerned, you can visit flippa to see how much a website is selling for. Even a starter website gets $200 or more. How much does it cost to build one website, not much if you are doing by yourself. While buying a website, tweaking it little and reselling can cost you money, when you build yourself and if you can also write contents, your cost is just the money you invested on the domain.