The term flipping implies a sale that is done in a flip, or in a quick and sudden manner. You cannot be considered a domain flipper if all you do is just list your domain names and wait for years for them to sell. At its core, domain flipping is about spotting the right opportunities at the right time, involving strategic buying and selling of websites for profit.
There’s an important distinction to make here between domain flipping and website flipping. The latter mainly refers to buying and selling full websites. By full websites, I mean websites that actually have content and more often than not have traffic and revenue. When buying and selling websites, the domain name matters less as the main value there is the content, traffic, revenue, history/reputation, sustainability and growth opportunities. The same can’t be said for domain names where you’re just selling “the name” and hence it’s all that really matters.