GLOs

Fraternities and sororities, or Greek letter organizations (GLOs)
https://en.wikipedia.org/wiki/Fraternities_and_sororities

While individual fraternities and sororities vary in exact organization and purpose, most share five common elements:

secrecy;
single-sex membership;
selection of new members on the basis of a two-part vetting and probationary process known as rushing and pledging;
ownership and occupancy of a residential property at which the undergraduate members of the fraternity or sorority live; and
use of a set of complex identification symbols including Greek letters, armorial achievements, ciphers, badges, grips, handsigns, passwords, flowers, and colors.

https://www.quora.com/How-are-letters-chosen-in-the-Greek-sorority-and-fraternity-system

The answers about the fraternity's letters are fine, but I learned a different rule for chapter designations. The first chapter is the Alpha chapter; the second is the Beta chapter. The chapters are named in the order of the Greek Alphabet. When the last letter has been used, the next chapter is the Alpha Alpha chapter. The one after that is the Alpha Beta chapter. Next comes the Alpha Gamma chapter. When the designation Alpha Omega is used, the next chapter is the Beta Alpha chapter, then Beta Beta, then Beta Gamma. All the Betas used? Gamma Alpha is next.

After about 600 chapters, the last double letter one being Omega Omega, one has to begin using three letter designation, the first being, you guessed it, Alpha Alpha Alpha!

I know of one fraternity which has a different system. The first chapter in a particular state is called the State Alpha chapter, so the first chspter in Iowa would be the Iowa Alpha; the second Iowa Beta. The first chapter of the same fraternity in Pennsylvania would not have to give way to the first one in Iowa. It would call itself Pennsylvania Alpha.

I have never heard of a chapter being allowed to invent its own name. Greek alphabetical order, please.

https://www.etymonline.com/word/chapter

https://www.washingtonpost.com/news/wonk/wp/2016/01/22/why-frats-can-throw-parties-but-sororities-cant/

https://en.wikipedia.org/wiki/Dionysus

https://en.wikipedia.org/wiki/Eleusinian_Mysteries

https://en.wikipedia.org/wiki/Mysteries_of_Isis

https://en.wikipedia.org/wiki/Ancient_Egyptian_religion

https://en.wiktionary.org/wiki/hear_through_the_grapevine

https://en.wikipedia.org/wiki/Ivy_League

https://www.socialmediatoday.com/content/strong-and-weak-ties-why-your-weak-ties-matter

https://abc.xyz/

https://en.wikipedia.org/wiki/Alphabet_Inc.

Greek letters are used extensively in math and science. Many Greek letters have standard meanings in math and physics. For example:

π, of course, is the ratio of the circumference of a circle to its diameter. It pops up all the time in physics.
ν - is the symbol for frequency
λ - stands for wavelength
θ - is usually an angle
ε - signifies a very small number
Δx - means a change in x (whatever x stands for)
η - usually stands for efficiency

And so on. If you study a technical field, you'll pick up the Greek alphabet as you go.

And as an added bonus, once you know the Greek alphabet, you know most of the letters in the Cyrillic (Russian) alphabet as well!

https://www.quora.com/Why-is-the-Greek-alphabet-important

https://www.quora.com/Why-is-it-important-that-the-Ancient-Greek-alphabet-was-the-first-to-write-vowels

https://www.quora.com/Why-are-Greek-letters-so-widely-used-as-symbols-in-physics-literature-when-English-letters-would-have-served-the-purpose-equally-well

https://en.wikipedia.org/wiki/Alphabet

https://en.wikipedia.org/wiki/Alphabetical_order