A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are used in various networking contexts and for application-specific naming and addressing purposes.
We can also say that a domain name identifies a network domain, or it represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a web site, or the web site itself or any other service communicated via the Internet.
Many WordPress hosting providers such as Namecheap will provide cheap domain registration with their packages. You can change the domain name location from one web host to another by changing its DNS settings. DNS settings basically tell the DNS servers which IP address corresponds to that domain name. When you change hosts, your IP address will change because you are changing servers.
There are many different domain name extensions that are available. Some of the most popular domain name extensions are: .com, .net, .org, .info, .edu. There numerous other country level domains such as .us, .in, .ly, .io, .ng and many more.