A URL is the address of a web page on the world wide web.

For example:

• The URL for the Trusts and Estates website is: trustsandestates.com
• The URL for the story We're Keeping Those Tax Breaks on the Trusts & Estates website is:
  trustsandestates.com/wealth_watch/tax-breaks-charity-deduction-obama-0325/.

Note the three parts to the URL:

• The website: trustsandestates.com/
• The primary category assigned to the article: /wealth_watch/
• The article slug: tax-breaks-charity-deduction-obama-0325/

Picking a primary category that contains more helpful keywords will help in search. The term "wealth" is more relevant than, for instance, the term "news."

This is also why selecting keyword terms for your slug is important. They will be indexed by the search engines and checked with other words on the page for relevancy.