Search Engine Optimization (SEO) is the process of improving the visibility of a website or a web page in a search engine's"natural," or un-paid search results.
In general, the higher ranked on the search results page, and more frequently a site appears in the search results list, the more visitors it will receive from the search engine's users.
SEO considers how search engines work, what people search for, the actual search terms or keywords typed into search engines and which search engines are preferred by their targeted audience.
Pay Per Click (PPC) (also called Cost Per Click) is an Internet advertising model used to direct traffic to websites, where advertisers pay the publisher when the ad is clicked. With search engines, advertisers typically bid on keyword phrases relevant to their target market.
PPC "display" advertisements are shown on web sites or search engine results with related content that have agreed to show ads.