URL stands for Uniform Resource Locator, but most people call it a web address. It's the name of your page after the WWW. How you name this makes a difference. I'm sure you have seen lots of gobbely gook like this:
What does all that stuff mean? Not much to the human eye, and often not much to search engines either. Google doesn't seem to like long URL's with the extra letters and numbers afterwards. As much as you can, make sure you keep these URL's simple and easy to read by humans and computers alike.
Do your URL's look like Alpha Bits cereal?