Freenom is a domain registrar which provides free domains under the TLDs of .tk, .gq, .ml, .cf, and .ga. Many hosts, both free and paid, use these domains, as they're too cheap to just buy a damn domain. Hosts which use free domains are shit, every single one of them, but that's beside the point of this PSA.
In case you run a small website or game server, you might choose to use a free domain from Freenom, thinking nothing of it, however, using them itself could pose a risk. Sites which receive a lot of traffic get taken over by Freenom, then turned into an adult film site, and after all that you would receive an offer from Freenom to get your domain back if you pay X amount of money. Just buy a domain and don't risk the domain being taken hostage, and therefore an important aspect of your community from being taken over and turned into something inappropriate.
Just buy a domain.