A domain name is a unique name that identifies a website. 
The Internet is based on IP addresses which are a series of numbers (such as 191.0.32.64) but, as it is hard to remember strings of numbers, domain names are used instead and serve as the address where online users can access web sites and other resources.
They operate under the Domain Name System (DNS),which translates the ‘easy-to-remember’ domain name into its IP address number and directs the visitor to the related website.
Domain names appear in URLs  in the address bar of the web browser. Each domain name is made up of a series of character strings (called "labels") separated by dots.
Every domain name has a domain suffix or extension. This is the last part of a domain name (the letters that come after the dot to the right of any domain name) and is often referred to as a top-level domain or TLD. The TDL indicates the type of website the domain name represents. For example ‘.edu’ is the suffix used to represent educational institutions. 
Some domain names end with a country code, such as ‘.ca’ for Canada, which identifies the location of the website. Popular TDLs include ‘.com,’ ‘.net,’ and ‘.org,’ but there are many approved by ICANN.