'Search Retargeting' as an example:

"Yahoo!’s Search Retargeting is a customized display targeting solution that lets advertisers capture user interest from search terms and retarget the user with display ads throughout the Yahoo! Network. For example, if a user searches for the keyword “sandals,” indicating strong purchase intent, an advertiser can target that user with a tailored display ad for footwear.
...."

http://finance.yahoo.com/news/Yahoo-Introduces-New-Ad-bw-14449462.html