I think Xidelt put it best.
It was very difficult for me to explain to my mother (who is British and attended university/medical school in Scotland) what a sorority is, why I wanted to join one, and what it meant to me then and means to me now. I think she understands certain aspects. For example, when she was in her first year at university, she was paired with a senior woman who helped her get acclimated to campus life, and she chose to be a senior woman later on - just like I had a big sister and a little sister. I explained to her that my sorority was involved with community service projects (I think that made her a little more comfortable with the idea) and that, while there is a social aspect to being in a sorority, and we would be having functions with fraternities, it didn't mean I'd be jumping into bed with random guys.

She's bought me a few AEPhi-related items, including a cloisonné giraffe, but I can tell ... she doesn't
get it.
My dad (who is American, and who attended a school where hazing in the greek system ran rampant) is highly anti-greek, and I am sure he colored my mom's perceptions. We had a brunch during parents' weekend, and my parents met all my sisters including my pledge sisters - and I think it put them at ease.
Anyway... I'd go with what Xidelt posted, with emphasis on the community service aspect.
And I'll stop blabbing now.