The URL (Uniform Resource Locator) is the address of a website. For example this URL is http://en.cship.org/wiki/URL.
Many censoring systems can block a single URL. Sometimes an easy way to bypass the block is to obscure the URL. It is for example possible to add a dot after the sitename, so the URL of this article would become http://en.cship.org./wiki/URL. If you are lucky with this little trick you can access blocked websites.
In the "How to Obscure Any URL" tutorial you can find many more ways of such tricks.