This article explains how Yahoo! Search orders the website search results.

Yahoo! Search results are ranked based on a combination of factors. One factor is how well the page contents match the search query. Another factor is how "Important" the page is based on its appearance as a reference in other webpages.

The match to the searched-for query terms is not just a simple text string match. It is a complex text analysis which examines the relationships and context of the words in the document. When determining how well a page matches a query, the full text content of the page, and the content of the pages that link to it are all taken into account.