I suppose I will have to spoon feed this to you. From the NATIONAL WEBSITE archives:
Zeta Tau Alpha is known as a fraternity, not as a sorority. The Founders intended Zeta Tau Alpha be designated a "fraternity" to distinguish the organization from the sisterhoods organized in connection with men's fraternities, called "sororities."
http://web.archive.org/web/200304210...a.org/trad.htm