A domain name is a registered right which entitles the holder to use a combination of letters and numbers (the domain name) to point to its web server. In other words, when you enter the domain name into a browser, you will be directed to the domain name owner's website or the website of someone who has a licence from the domain name owner. In practice, it can be bought and sold, like a piece of property. Currently in the UK there are no formal requirements for domain name sales or transfers to be evidenced in writing, although the domain name registrar will have their own transfer process which must be followed. Nevertheless, it is sensible to have a written agreement so that appropriate warranties and assurances are given.
The transferor of a domain name will be registered as the owner with the registrar of the top level domain. (Nominet UK is the registry for internet domain names ending in .uk.) For basic public information on the domain name system, how it works and how to obtain global top level domains (gTLDs) such as ".com", ".org" etc. see the The Internic website.
For basic public information on the UK top level domain, see Nominet UK.
Since domain names are subject to registration, their transfer takes effect by re-registering in the name of the transferee.
Domain name registries require fees to be paid when registrations are transferred. Nominet transfer fees are currently £10.