The Answer:

We'll let the people at Yahoo! explain where the name came from.

The Web site started out as "Jerry and David's Guide to the World Wide Web" but eventually received a new moniker with the help of a dictionary. The name Yahoo! is an acronym for "Yet Another Hierarchical Officious Oracle," but Filo and Yang insist they selected the name because they liked the general definition of a yahoo: "rude, unsophisticated, uncouth." Yahoo! itself first resided on Yang's student workstation, "Akebono," while the software was lodged on Filo's computer, "Konishiki" - both named after legendary sumo wrestlers.

—The Fact Monster