A fraternity is a society, usually at an American college or university. The word "fraternity" comes from the Latin frater ("brother"). Fraternities are also called Greek-letter societies because most of them have Greek mottoes and use the first letters of the words as their name. Some fraternities are social in nature, and others are professional or honorary. Fraternities may be for men or women or both. Women's fraternities are usually called sororities. Many social fraternities are national organizations with many local chapters, and include both undergraduate and alumni members.

   Membership in social fraternities is by invitation. In most colleges that have fraternities, there is a rushing period during which each fraternity invites freshmen to parties. From these a fraternity chooses a number of pledges and assigns them many tasks to prove their interest and to determine whether they would be good members. At the end of this hazing period the successful pledges are initiated into the fraternity in a secret ritual that includes an oath, a special handclasp, and the receipt of a fraternity pin.

College fraternities now stress campus activities far more than secrecy. They compete in sports and academic work, support candidates in college elections, and may give scholarships to members. Fraternities have been criticized, however, as being snobbish and discriminatory. Many people think that members have too little contact with persons of different backgrounds. The National Interfraternity Conference was formed in 1909 to maintain standards and consider reforms, and reforms have been made by many individual fraternities and local chapters.
Honorary and professional fraternities also have national and local organizations, in which membership is based on academic achievement. Phi Beta Kappa is an honorary society that accepts those who have a high general scholastic record, and Sigma Xi accepts those proficient in the sciences. Members of Alpha Omega Alpha belong to the medical profession, and Tau Beta Phi is for engineers.

   The first fraternity, Phi Beta Kappa, was founded in 1776 at the College of William and Mary in Williamsburg, Va. Its purpose was originally social, but it later became honorary. The pattern for modern social fraternities was set by three groups founded at Union College in Schenectady, N.Y., in 1825 and 1827.

   Most of these early fraternities began as literary and debating societies that gradually expanded their activities and spread widely in the 19th century. By 1950 there were 60 social and more than 100 professional fraternities in the United States. Recently high school students have formed fraternities, but these organizations are not recognized by colleges and have been declared illegal by many states.