The last and most significant component of an Internet fully qualified domain name, the part after the last ".". For example, host wombat.doc.ic.ac.uk is in top-level domain "uk" (for United Kingdom).
Every other country has its own top-level domain, including ".us" for the U.S.A. Within the .us domain, there are subdomains for the fifty states, each generally with a name identical to the state's postal abbreviation. These are rarely used however. Within the .uk domain, there is a .ac.uk subdomain for academic sites and a .co.uk domain for commercial ones. Other top-level domains may be divided up in similar ways.
.com - commercial bodies .edu - educational institutions .gov - U. S. government .mil - U. S. armed services .net - network operators .org - other organisations
Since the rapid commercialisation of the Internet in the 1990s the ".com" domain has become particularly heavily populated with every company trying to register its company name as a subdomain of .com, e.g. "netscape.com" so as to make it easy for customers to guess or remember the URL of the comany's home page.
Several new top-level domains are about to be added (Oct 1997): .nom - individual people .rec - recreational organisations .firm - businesses such as law, accounting, engineering .store - commercial retail companies .ent - entertainment facilities and organisations