Wikipedia
Fraternities and sororities
Fraternities and sororities (from the Latin words and , meaning "brother" and "sister" respectively) are fraternal social organizations for undergraduate students. In English, the term refers mainly to such organizations at colleges and universities in North America, although it is also applied to analogous European groups also known as corporations. Similar, but less common, organizations also exist for secondary school students. In modern usage, the term Greek letter organization is often synonymous with the terms "fraternity" and "sorority".
Typically, Greek letter organizations are single-sex, initiatory organizations with membership considered active during the undergraduate years only, although a notable exception to this are historically black, latino multicultural, and professional fraternities, in which active membership continues, and into which members are often initiated long after the completion of their undergraduate degrees. Greek letter organizations may sometimes be considered mutual aid societies, providing academic and social activities. Some groups also maintain a chapter house, providing residential and dining facilities for members.
Terminology
In modern usage, the term Greek letter organization has become synonymous with the North American fraternity and sorority. The term fraternity, often colloquially shortened to "frat" (though use of such term may be derogatory in some contexts), typically refers to an all-male group, while the term "sorority" typically refers to an all-female group. However, some womens groups define themselves as fraternities for women or womens fraternities, such as Alpha Gamma Delta, Alpha Delta Pi, Phi Mu, Alpha Omicron Pi, Alpha Xi Delta, Delta Delta Delta, Kappa Alpha Theta, Zeta Tau Alpha, Alpha Phi, Delta Gamma, Pi Beta Phi, Sigma Alpha Iota, Kappa Kappa Gamma and Chi Omega. Additionally, some groups that define themselves as "fraternities" may be mixed-sex, such as Phi Sigma Pi or Kappa Kappa P read more at » http://en.wikipedia.org/wiki/Fraternities+and+sororities