Do you really only have one URL for each page of your website? Many websites (the ineedhits site included) actually contain several URLs for the same page. This mainly happens with homepages. Here’s an example:

www.yoursite.com
yoursite.com/
www.yoursite.com/default.aspx
www.yoursite.com/index.html

can all refer to the same page, although they are technically different pages that, as far as search engines are concerned, may contain different material. Google calls this type of URLs “canonical URLs”, and the search engine then needs to decide which one of these URLs to index. Picking the most appropriate of these URLs is called “canonicalization”.

How Can You Make Sure Google Indexes the Right URL?

Matt Cutts from Google has given the following advice on canonicalization:

Firstly, make sure that all your internal linking points to the URL that should be indexed. So, if you want www.yoursite.com/default.aspx to be indexed, point all your internal links to this URL, but not to www.yoursite.com.

Secondly, add a permanent (301) redirect that points to the page that should be indexed. For the example above, set up a 301 redirect on your webserver for www.yoursite.com that redirects to www.yoursite.com/default.aspx.

What Not to Do

Google’s Webmaster Help Center contains detailed information on what to do if you want to remove your whole website or parts of it from Google, and also offers a URL removal tool. Do NOT use Google’s URL removal tool on canonical URLs, since Google may accidentally remove your whole website for half a year. Don’t even think about doing this!

Where to Find Out More

Read Matt Cutts’ full post on SEO Advice: URL Canonicalization.
Read up on the difference between 301 and 302 redirects in DIY Tip: Search Engine Friendly Domain Redirects.
Read Wikipedia’s article Canonicalization.