Fraternity Greek letters are traditionally two or three letters that represent the motto of a fraternity. In some fraternity names, the Greek letters are the initials of the words making up their Greek motto. Some other fraternity names choose the letter combination for their symbolic meaning.
The first fraternity, a male student society founded at the College of William and Mary in 1776, was Phi Beta Kappa. The Greek letters Phi Beta Kappa were the initials of their motto: Philosophia Bios Kybernethes, which roughly translates to “Philosophy is the guide to life.” When first founded, Phi Beta Kappa kept its identity and motto secret. The fraternity only disclosed its constitution in 1831.
The popularity of Phi Beta Kappa led to the creation of other fraternities who also referred to their organizations using Greek letters. Some examples are Sigma Phi, Delta Phi and Phi Sigma Kappa. These organizations found inspiration in their educated elite members, using letters from the Greek language, the symbol of intellectual standing.
Some fraternity mottos are secret, with the organization choosing not to disclose the reason behind the letter combination choice, at least to the public. There are also exceptions of fraternities that do not choose Greek letters as names, such as The Skull and Bones, the Seal and Serpent, or the FarmHouse.