As of today, the contextual search technology behind
available as a Web Service. Fundamentally, this means you can provide
some text as context in addition to your explicit query.
This can be very useful in resolving ambiguous queries. For
example, if you use href="http://developer.yahoo.net/web/V1/webSearch.html">our Web
Search service to provide web search on your scuba diving web site
you might provide a few words or sentences about scuba diving in
addition to the user's query. If a user searches for "equipment" with
this context as background, they'll find more relevant results than a
plain web search for "equipment".
Y!Q also works well on content heavy sites such as news or blogs.
Article titles or lead paragraphs often work well as context for
focusing queries beyond the explicit keywords.
Web Search documentation for API details and a an example using
renaissance art context to get at the right results for a "madonna"
Yahoo! Search Web Services