Keywords buying is the practice by which an advertiser can ensure himself of a favorable position in search engines results pages by bidding on a keyword.
An advertiser’s ad is displayed when a query matches the keyword. The advertiser is usually charged for the bid sum when the ad text is used (or clicked) by an Internet user.
The most famous and dominating keywords buying program is Google’s Adwords.
The ad texts with keyword buying are called sponsored links.
Keyword buying was introduced by Google Adwords :