Here I will explain about the difference between contextual advertising, placement-targets advertising and Interest-based advertising.
Contextual advertising: A contextual advertising uses advanced algorithms to analyze content of the page and shows advertisements based on what the user is viewing. For example, if the user is viewing a site about technology which uses contextual advertising, user might see ads related to technology.
Placement-targeted ads: Placement-targeted ads serve up contextual ads to web users based on the specific sites they are visiting. It allows an advertiser to select specific publisher sites on which to run their ads and also target individual spots.
Interest-based advertising: Interest-based advertising or behavioral advertising serve up ads to web users based on their previous online activities (based on their interest). Previous online activities are stored in the browser advertising cookie, which is used to display interest-based ads. Learn about How Google Interest-based Ads Works.