Pay per click (PPC) is an advertising model used on search engines, advertising networks, and content websites/blogs, where advertisers only pay when a user actually clicks on an ad to visit the advertiser's website. Advertisers bid on keywords they predict their target market will use as search terms when they are looking for a product or service. When a user types a keyword query matching the advertiser's keyword list, or views a page with relevant content, the advertiser's ad may be shown. These ads are called a "Sponsored link" or "sponsored ads" and appear next to or above the "natural" or organic results on search engine results pages, or anywhere a webmaster/blogger chooses on a content page.
Advertisers using these bid on "keywords", which can be words or phrases, and can include product model numbers. When a user searches for a particular word or phrase, the list of advertiser links appears in order of the amount bid. Keywords, also referred to as search terms, are the very heart of pay per click advertising. The terms are guarded as highly valued trade secrets by the advertisers.