This is a term related to PPC in situations where Google determines that an advertiser is sending people who click their ad to a page that is not related, is poor in quality, or even loads too slowly.
Google Slap is the action they take to discourage this behavior and may result in advertisers having to pay a higher CPC as well as possibly reducing your PR.To avoid the Google Slap advertisers need to work to achieve a high Quality Score.
