Pay per Click ( PPC )
When you use some words (keywords) in a search engine you are presented with a page of search results which include both "natural" and "paid" results.
Each major search engine has a version of paid advertising. Google's advertising is called Adwords and is by far the most popular. Although there are a variety of options, Adwords is fundamentally a Pay-Per-Click (PPC) system where you only pay if someone clicks on your ad.
The natural search results cannot be paid for. You can increase your rank by including content on your site that people are actually looking for and implementing an effective search engine optimization (SEO) program.