- .com and .co
Means company or commercial. .com is the most common domain extension and indicates either a business or commercial site.
- .uk.com and .co.uk
As above but preferred by businesses that mainly operate in the UK.
Means business. A less popular version of .com.
Means organisation and indicates various community organisations, charity, non profits, etc.
Means networks and is often used by network-related businesses or an "umbrella" website that acts as the portal to a set of smaller websites.
- .uk.net or .gb.net
As above but preferred by network-related businesses or "umbrella" websites that mainly operate in the UK or Great Britain.
Means TV/Television and is mainly used by TV channels but is becoming increasingley popular with websites that regularly post videos, almost like an online TV channel.
- .me and .me.uk
Means "me" as in you! Intended for use for personal websites.
Means a limited company in the UK. The name registered must match the company name so Acme Widgets Limited can only register acmewidgets.ltd.uk. Any other variation, including trading names, will be rejected by the registry.
Means European Union and as its name implies it is intended for use by any company or organisation in Europe.
Means telecoms and is intended for use by companies and organisations that provide telephony or Information communications services.
Other common top-level domains are actually country codes, such as .us for United States, .uk for United Kingdom, and .au for Australia.