According to WebHostingReport.com, Yahoo! is an acronym for Yet Another Hierarchical Officious Oracle. The original name was "Jerry and David's Guide to the World Wide Web," named after Jerry Yang and David Filo, the founding members of the company.
Yahoo! includes an exclamation mark in its name because there were already other companies named Yahoo. With this unique identifier, the founders were able to trademark it. Yang and Filo's original guide was simply a collection of websites they found interesting. This list became so long, it had to be broken up into categories. As of 2013, Yahoo! has grown to become the second most visited website, according to data published by Business Insider.