What would be the proper terminology for dress code for a high school
reunion, we want it to be casual, yet no sloppy cutoff's, beach wear. 
Events are a Welcome gathering, cocktails and hors d's one night and a
dinner followed by a platter party with disk jockey the 2nd night. 
Someone suggested Business Casual, I feel this is not exactly
appropriate for a high school reunion.  Dressy casual is too dressy. 
I have seen "smart casual", "upscale casual", informal, wondering if I
could say something original, "This is a casual weekend, Friday night,
wear nice clothes, Saturday night put on your dancing shoes and dress
to rock and roll. (50's attire if you wish). Oh, I"ve also seen semi
dressy casual.  People can wear blue jeans if they want, just want
them to know it's not a dress up kind of weekend, nor a dress down. 
Thanks very much.

Hi there!

The problem with looking for something original when you want to
convey what is expected of people is that they may interpret it as
something entirely different.  Even the venerable Miss Manners
(mundanely known as Judith Martin) has an opinion on such originality:

"MISS MANNERS:

A friend of mine just got an invitation to a fancy affair and the
dress code was indicated as "fire and ice."

We're not sure what he and his wife should plan to wear.

GENTLE READER:

Red and white? Blue-red and transparent? Heavy-duty raincoats? Miss
Manners suggests your friend call his hosts and ask.

If people insist on making up cute costume codes, she declines to act
as their translators."

Miss Manners
http://www.jsonline.com/lifestyle/advice/jul03/152087.asp

Ouch.  But who can blame her?  She also says in "Miss Manner's Guide
for the Turn of the Millennium" (Pharos Books, 1989, page 443:

"Hosts cannot be coy about telling people what to wear."

Help your guests avoid the head scratching, "what does this mean we
should wear" confusion, and tell them what you want.  If business
casual (which is what it sounds like you want, but without actually
having to use that phrase) doesn't sound appropriate to you, consider
these:

-- preppy casual
-- evening casual
-- country club casual
-- classy casual

These all imply a neat, polished look, without being stiff and too
formal, and they let your guests know what is expected of them without
requiring a translator.

Good luck!

--Missy

Search terms [ "dress code" "Miss Manners" ]

I like the sound of "classy casual." To me, this expresses
"comfortable, but not grubby," which I presume is what you're trying
to convey.