Most businesses also run their own DNS servers. In the very least, this is needed to resolve names of internal hosts. Anything from naiming and computer, nais-latpop, to being able to refer to a printer by a name instead of an IP requires your own name server.
Third option is to use a DNS as a service provider. You can test DNS functionality as well as backup DNS options in case you experienced problems with your own. You might even be in the early stages of building out a new network and even if you plan to have. your own name server, eventually, it may not be ready for user.
Some internet organizations run what are called public DNS servers, which are name servers specifically set up so that anyone can use them for free.
In ancient sysadmin lore, it’s said that for many years the most commonly used public DNS servers, were those run by Level 3 communications.
One of the largest ISPs in the world. Level 3 is fact so large. They mostly do business by selling connectivity to their network, to other ISPs that actually deal with consumers, instead of dealing with end-users.
The IP addresses for Level.3’s public DNS servers are 4.2.2.1 through 4.2.2.6.
Google at 8.8.8.8 and 8.8.8.4