AdWords

Google AdWords is an online advertising service that enables advertisers to compete to display brief advertising copy to web users, based in part on keywords, predefined by the advertisers, that might link the copy to the content of web pages shown to users. Web pages from Google and from partner websites are designed to allow Google to select and display this advertising copy. Advertisers pay when users divert their browsing to seek more information about the copy displayed, and partner websites receive a portion of the income they generate.

AdWords has evolved into Google's main source of revenue. Google's total advertising revenues were USD $43.7 billion in 2012. AdWords offers pay-per-click (PPC), that is, cost-per-click (CPC) advertising, cost-per-acquisition (CPA) advertising, cost-per-thousand-impressions or cost per mille (CPM) advertising, site-targeted advertising for text, banner, and rich-media ads, and remarketing (also known as retargeting). The AdWords program includes local, national, and international distribution. Google's text advertisements are short, consisting of one headline of 25 characters, two additional text lines of 35 characters each, and a display URL of 35 characters. Image ads can be one of several different Interactive Advertising Bureau (IAB) standard sizes.