The aim of Google AdWords is to provide the users with a positive experience when they click on the Google AdWords ads. To achieve this Google AdWords have a link policy that provides guidelines on the following topics:
The Display URL:
The display URL is the fourth line in your text ad. This URL must give the user a good indication of the actual destination URL. It does not need to be exactly the same but similar. For example using a Display URL: www.bigbooksstore.com and a Destination URL: http://www.amizon.com/books.html will not be allowed. The Destination URL must be something along the lines of http://www.bigbooksstore.com/indes.html.
The destination URL is the actual landing page of your text ad. This web page has to work properly (no typos in URL). The page is also not allowed to be under construction. The destination URL must also be an html page so that no additional software will be required by the user to view your page for example Acrobat Reader.
The back button on the landing page must allow the user to return to his previous Google search results. Your ad will not be approved if the back button on your landing page does not work properly.
Pop-ups or pop-unders:
Pop-ups or pop-unders are defined by Google AdWords as any additional page that opens other than your landing page. The Google AdWords policy does not allow any pop-ups or pop-unders when entering or leaving your landing page. Users find them distracting and this leads to a poor user experience.