"Behavioral targeting is a technique
used by online publishers and advertisers to increase the
effectiveness of their campaigns. Behavioral targeting uses
information collected on an individual's web-browsing
behavior, such as the pages they have visited or the
searches they have made, to select which advertisements to
display to that individual. Practitioners believe this helps
them deliver their online advertisements to the users who
are most likely to be influenced by them. Behavioral
marketing can be used on its own or in conjunction with
other forms of targeting based on factors like geography,
demographics or the surrounding content." -- wikipedia.com
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a list with more information about Behavioral Targeting. Check it out.