PPC is a paid service offered by search engines that provides immediate results. Your ad is featured on the search engine, and you pay the host only when someone clicks on your ad.
With the use of PPC, your search engine ranking depends on how much you bid for each keyword rather than the quality of your content. PPC can also be used in the interim when you are waiting for your website to get better SEO rankings. Some companies use both PPC and SEO together to capture maximum real estate of the first page of search engine listing to drive out their competitors ad to the next pages.