@SybilTheSpy
They are an important rite of passage for middle class African American girls, along with debutantes balls. They came about as African Americans tried to shake off negative stereotypes, particularly those associated with African American women.
There are debutantes balls (aka charity events involving the well off) in many cities, but they're a bigger deal in the South than anywhere else.
They're basically an introduction to the ladies who lunch set and the country club lifestyle, preparing young women (and their male escorts) to take their place on committees that run charities, do a huge amount of fundraising for local and national charities in areas like the arts, education, hospice, etc., which is mainly accomplished by developing connections, engaging in a social whirl that they organise, which generates charitable contributions.
I noted that Apple Martin has joined a sorority at Vanderbilt - Kappa Kappa Gamma (aka Visa Visa Mastercard). Cotillions and debutantes balls are nothing compared to sororities and sorority life, Rush week, etc. I don't think anything like American style fraternities or sororities exist anywhere else. There is an entire vocabulary associated with frats and sororities that is pretty much unknown outside of the US.
One of my DDs pledged a sorority, for reasons I still can't fathom.