domain extension.An example of a domain extension which is an Internet category is .com for commercial, .org for organization, .gov for government, .edu for all educational institutions, .mil for military or .net for a network. An example of a domain extension which is a country code is .us, .uk or .de.
Domain extension is the internet category such as .com, .net, .in, etc. In this, he domains extensions are putted over the right side of the url after the dot. They can be used for all such organization, like educational, research, business, etc.