The top-level domain or TLD is the last part of a domain name: .com and .us are examples. .com is the most popular and memorable TLD, and is what is called a generic TLD (gTLD). Generic TLDs are, in theory, for particular classes of organisation, although in practice the lines have become blurred. When the system was first designed, the intention was to give users a hint as to the nature or purpose of a website by way of its TLD. For example, .com was supposed to refer to commercial websites, whilst .org was intended for non-profit organisations and charities. There are still rules in place on some TLDs which restrict who can register those domains, in order to maintain this structure. For example, in for the registration of a .biz address, there are stringent checks to verify that the applicant is affiliated with a legitimate business. However, in many cases, the most popular TLDs such as .net, .com and .org have become unrestricted and are used by all sorts of different registrants.

Some gTLDs are sponsored, meaning that they are proposed, administrated and sold by an independent organisation. .mobi is a recent example of a newly-developed sponsored TLD, intended for sites aimed at users of mobile devices. Others include .museum (for legitimate museums) and .cat (for sites related to the Catalan language and culture). These sponsored domains usually require the fulfilment of various criteria before a domain can be registered.

The other main category of TLDs is the country-code TLD (ccTLD). These are two-letter affairs which are intended to indicate the country of origin of the corresponding websites. For example, .de is the German ccTLD, and can only be registered by those who live or trade in Germany. However, many ccTLDs are open to be registered by anyone in the world, which again undermines the intended system. For example, .tv is the ccTLD for Tuvalu, but is increasingly being used by television broadcasters, and .fm is the ccTLD for the Federated States of Micronesia, but is often used for FM radio stations. Also, domain names ending in .tk, the Tokelau ccTLD, can be registered for free by anyone in the world.

So which TLD should you choose when registering a domain name? If your site is for business purposes, .com will be the easiest TLD for your customers to remember. Many browsers default to .com if the user omits the TLD when they type an address, and people are likely to assume that your address will end in .com. Many internet users seem unaware that other TLDs even exist! Also, choosing a .net or .info address can give some visitors the impression that you couldn't get hold of your own name, which may well be the case, if you've had to resort to some other TLD than .com.

However, a ccTLD can be valuable if you're a local trader, or if you have several sites for differently located branches of your business. Many visitors are reassured by a local ccTLD, and feel that your service will be specifically tailored to their needs. For example, a user from the UK might feel happier browsing a .co.uk site because the site is more likely to use British rather than American English.

If you register a TLD which is anything than .com, try to avoid one that is already held as a .com address. This is because you will invariably get visitors mistakenly typing .com instead of your TLD, and that means you will be handing free traffic to the owner of the .com – especially galling if they are your competitor!

By Natalie Catchpole