This graph shows organic search engine result visits for the period from Google. Please note that if you are running a PPC advertising campaign with Google, then you will need to ensure your advert's URLs are set up properly with URL tracking so that your PPC paid click-thrus are not reported as organic non-paid click-thrus. This is really easy to do in Google Adwords, simply ensure that 'Auto-tagging' is turned on.
For further information on how to set up PPC tracking correctly with Google please visit our SEO blog on the subject.