Domain name is a meaningful, easy to remember the name for your WordPress website. Generally, each computer on the internet is uniquely defined through IP Address which is a complex alphanumeric number. The computer on witch your WordPress is hosted also has a unique number define called IP address. You can take your server IP Address from your hosting provider. A human brain is not very suitable to remember numbers, so to simplify the things and make the address easy to remember domain name is assigned to IP address. The server that collects and store the information of IP address and their corresponding domain name are called DNS Server. There is a number of DNS server in the world works I cooperation with each other to the covert domain name to IP Address whenever needed. If you want to understand more about the DNS and IP address: IP address And DNS
There are so many companies where you can search and buy your unique domain name as I have as travlendtech.com . Some of the top rated company where you can buy are GoDaddy.com , Namecheap.com, Bluehost.com, HostGator.com, Name.com . you can also buy domain from google but at the time of writing this article it is in the beta stage .
Freenom where you can get a free domain for three month . The domain name extension that they provide for free are .tk/.ml/.ga/.cf/.gq .
absolutely free domains