The organization ICANN (Internet Corporation for Assigned Names and Numbers) is in charge of domain names, and they do not allow the
permanent registration of domain names. You must pay an annual fee to
maintain your domain name. As long as you keep buying your own domain, no one can take it away from
you, but if you do not pay it can be put up for grabs by pretty much
anyone who wants it. It’s a very common, but shady practice done by
people looking to make a quick buck. Just like during elections when someone buys a candidates name as a domain and then try to sell it to the campaign headquarters for a hefty fee. I am not sure, but, I believe that type of domain owning has been banned, you would need to research that.
So if you do buy a domain, keep up with it, and as long as you keep paying for it, its yours to keep.