If this option is selected, then the start and end of a URL must match those given, but there can be anything in between. This option also allows you to block an entire site.
e.g. Specify annoying/ in the first field to block both http://www.foo.com/annoying/picture.gif and http://www.foo.com/annoying/very/advert.html. If left blank, the path can start in any way at all. The second field specifies the end of the path to block (e.g. you may specify .gif to block only .gif pictures which also match the other criteria).