The domain is the name of the web site. To reserve a particular domain you must reserve one (it cost approximately 35USD). It is highly recommended that it should be short and easy to spell. The site should make voters able to guess the fact that this page belongs to you, for this reason it should avoid initials, numbers or words in a confusing way.
Take into consideration
Keep your website name short. Make it distinct, short, and easy to spell. It is recommended to use 12 or less characters.
Easy to spell.
Avoid using initials. Use the version of the name that is simplest and most easy to remember.
Make it clear. Avoid using numbers in a confusing way or odd words. It is important that when people look at your website they should be able to guess that it belongs to you and not to someone else.
Chose ".com" and not ".org" or ".net". The rational behind this is that most browsers automaticaly go to the ".com" address unless another suffix is specified.