Absolute & Relative URL

Understanding Absolute and Relative URL Addresses

1. What is an absolute URL?
2. What is a relative URL?
3. How can an absolute URL be made relative?
4. Programmatic Access to Relative URLs
5. Converting relative and absolute URLs

For the above questions please refer below link.

http://msdn.microsoft.com/en-us/library/bb208688%28v=office.12%29.aspx