This is my understanding of the word "soror"
1. it is only used by members of particular sorority to greet other members of that PARTICULAR sorority. "Soror" is never used as a term for people that are not part of your sorority. I have never heard it used that way. When I hear the word "soror" I know it means a member of a Sorority, Inc., and nothing else.
2. (and this may not be the case) it is only used as a greeting between members of BLACK BGLO'S. Greeks consider the use of "frat" of "soror" disrespectful to the black orgs that originated those sayings in this context.
I hope this has been some clarification.
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In complete darkness we are all the same... It is only our knowledge and wisdom that separates us... Don't let your eyes deceive you
The Diva Truth