Slang term adapted by the media to describe the Yahoo and Microsoft search partnership. The partnership will see Microsoft power Yahoo's search business with its search engine, Bing, while Yahoo will handle search ad sales, using Microsoft's AdCenter technology to manage ad flow.
See "Does MicroHoo Have Staying Power?" on Internetnews.com.
See also "Web Search Engines & Directories" in the Quick Reference section of Webopedia.