The term TLD is short for 'top-level domain'. It refers to the suffix at the end of a domain name URL. For the domain name 'http://www.mysite.co.uk' it refers to the 'co.uk' section of the URL. The amount of TLD's are always been added to and predefined. Currently some of the most popular ones are,

• .com - commercial
• .uk.com - commerical in the UK
• .co.uk - UK
  
• .gov - government
  
• .edu - educational
  
• .org - organizations
  
• .net - network