SEO is the process of affecting the visibility of a website or a web page in a search engine's "natural" or un-paid ("organic") search results.
PPC is an Internet advertising model used to direct traffic to websites, where advertisers pay the publisher (typically a website owner) when the ad is clicked. With search engines, advertisers typically bid on keyword phrases relevant to their target market. Content sites commonly charge a fixed price per click rather than use a bidding system. PPC "display" advertisements, also known as "banner" ads, are shown on web sites or search engine results with related content that have agreed to show ads.
I think wiki will help ya