Which is correct?
1. The Blah Blah Chorus is a women's acappella chorus.....
2.The Blah Blah Chorus is a womens acappella chorus....
I have to go back over a thousand years to explain this one.
In Old English, long before the Norman Conquest in 1066, many nouns formed plurals without adding S or ES. Instead they added "en." Because some of these are very common words, we still follow the old usage:
Woman->Women (singular "wifman," meaning "with man")
Chick->Chicken (no kidding! "I own six chicken" was once the way you'd say it.)
Later we began to form more familiar plurals by adding S. And we showed possession of a singular noun by adding 'S, while a plural would be S'—for example, Crawford Kilian'S blog, and the KilianS' house (which belongs to my wife as well as me).
Why don't we say "human" and "humen"? Because "human" comes from the Latin "humanus" (made from humus or earth).
So what to do with these Old English plurals? We treat them as if they were singulars:
Men's clothing (clothing belonging to men)
Children's toys (toys belonging to children)
Women's chorus (chorus belonging to women)
By the way, I should add one more point. Marge writes "acapella chorus," but it should be "a capella chorus." "A capella" means "in the style of the chapel" (capella)—where people would sing religious songs without musical accompaniment. Sometimes, to explain English, we have to explain Italian and other languages!