Google AdWords is an online advertising service that places advertising copy at the top or bottom of, or beside, the list of results Google displays for a particular search query. The choice and placement of the ads is based in part on a proprietary determination of the relevance of the search query to the advertising copy. AdWords has evolved into Google’s main source of revenue.
The AdWords program includes local, national, and international distribution. Google’s text advertisements are short, consisting of one headline of 25 characters and two additional text lines of 35 characters each. Image ads can be one of several different Interactive Advertising Bureau (IAB) standard sizes.