One name for the attire is "business casual." You might mention at the bottom of the invitation "Business casual attire requested." If you include an RSVP number, those who don't understand should be able to ask when they respond.

I've also seen "dressy casual" - but what the heck does that mean?

If I were invited to the rehearsal dinner, I'd expect the attire to be a nice enough dress, or nice pants, for the women, and sports jackets or nice shirts & pants for the men.

So I'd probably just leave off any mention of formality of attire. In my circles, nobody is going to show up in jeans, and nobody is going to show up in a black suit or long dress or cocktail gown.

They'll come in whatever they wore to work, or maybe they'll spiff up slightly.

Maybe your circles would need more guidance; if so, "semiformal" if the official terminology. Emily Post has this explanation:

"'Semiformal' on invitations to a party means "no jeans or T-shirts." Women wear dresses or "good" slacks--men wear sport shirts and slacks rather than jeans."

Unfortunately, today the younger generation and some of the older ones as well, will show up, even at a wedding held in a cathedral, wearing jeans and even shorts. Perhaps they were raised without an awareness of proper dress and protocol. I have had older couples show up at a sit-down dinner reception dressed in shorts looking like they just got into town after a long car trip. I have also had guests banned from entrance to weddings held at country clubs and other social clubs because they were improperly dressed. It seems that today, anything goes and people don't take the time to show respect for their hosts by dressing appropriately.

Sweeby, I hate "dressy casual"! To me, that translates to, "Casual, but we don't trust you not to show up in ripped jeans and a filthy T-shirt."

sweet pea says that that is indeed what some people do. Well, maybe so -- but (especially given that those people probably would dress that way no matter WHAT you put on the invitation) I wouldn't insult the other guests by indicating that assumption.

Personally, I don't think I'd write anything other than "black tie," "dressy," or "casual," on an invitation, and and I really hate "original" things like "festive casual" or "celebratory attire" -- they are just plain confusing, and they sound like the hosts are trying too hard. We recently went to a wedding the invitation to which said, "No neckties!" I know the couple wanted it casual, and they probably thought the wording was cute, but I felt that was just plain bossy and controlling. Some of the older male guests (including the groom's father) feel very uncomfortable NOT wearing a tie to even a casual event (not a picnic or softball game, but you know what I mean). They could just have written "casual" and everyone would have dressed appropriately, and if some men wore ties, so what? Beats antagonizing your guests before the wedding even starts. You can dress your bridal party to match (and, ironically, they DIDN'T), but not your guests!

In fact, I am more and more not writing anything at all. The style of the invitation and the time, type, and location of the event really give anyone who cares all the information they need.

Suppose you got an invitation with paper and font that are pretty but dignified, a (readable) script font, and fairly formal wording:

Please join us for
Rehearsal dinner
Saturday, June 31
7:30 pm
La Palma Ristorante / at our home
123 Main Street
AnyTown
Muriel and Waldo Quilter
RSVP: (000) 555-1212

or this one, on day-glo paper with a border of balloons and a goofy font:

WOW!!!
With just 24 hours to go, let's pull out all the stops and have a bash in honor of Petunia and Cuthbert!
Clambake -n- kegger
Saturday, June 31
Party Beach
7:30 p.m.-???

Wouldn't you know how to dress for each of these parties, without being given a dress code?

For your party, quilter, I would either write nothing regarding dress, or, if you feel that it is still ambiguous (like if it's at a home), then I would write "casual." If the invitation is anything but ultra-casual, people will know to dress decently. No one is going to wear dressy party clothes. If someone wears nice jeans and a nice top, and someone else is in a suit, it isn't a disaster -- after all, you might very well see both at a good restaurant. The guests don't have to match each other exactly, and you don't want to risk casting a pall on your party by appearing overly controlling of the guests' clothes.

HELP - For my son's rehearsal dinner I want to ask guests to bring a written memory (I am supplying the "ornament") to hang on a Memory Tree...I want to write something cute asking this but my mind is totally blank...any ideas greatly appreciated....

Future MIL, that is a WONDERFUL idea. Do you mind if I borrow it for my son's rehearsal dinner?

You know, I think you are better off not having "cute" wording for your request. It is a lovely, sweet, moving idea. Cute very quickly becomes cutesy, and it also can get confusing when clarity is sacrificed for gimmick.

I would just put a note on the invitation something like this:

Please use the enclosed ornament to record a favorite or funny memory about Cuthbert or Petunia for a "Memory Tree."

I think that it will be perfectly obvious.

A warning: although I LOVE something like this, it's surprising how many people just won't do it. My husband did a similar thing for my 50th birthday (an album, not a tree). A few of my closest friends didn't send anything, and some people I hardly know went to the trouble of writing poems, doing funny mock-ups, etc. Anyway, for those people who are reluctant or self-conscious, cute wording is just going to put them off even more (they will find it pushy).

I agree with gellchom...it's a great idea and you should keep the wording simple and direct.

What type of ornament were you thinking about using?
The first image that came to my mind was a round (or any other shape) plastic or metal ornament that opens up so that a folded piece of paper could be put inside.

If you want, you could request that the guests mail you their memory so that you could insert them into the ornaments ahead of time. At the rehearsal dinner you could have a few extra ornaments on hand in case some guests bring their memory with them. Also, have some papers and a pen near the tree so guests who totally forgot, could write one out at the venue.
One other idea...you could remind them to sign their name.
90% of the memories will not need names. BUT, I could see the bride & groom reading a couple of them and tipping their heads and saying "Who wrote this?"

I must admit, my first thought was, "Nooooo, not "cute"." I'm in the "just say it" camp :-)
The idea itself is good, if you know the bride and groom would appreciate it. Another option if you think the ornaments might end up in a box in the attic is a memory book.

Oh, right, have them send them ahead of time, or at least send them the blank "ornament" in advance to bring with them. They will write much better stuff if they have some time, and some will even decorate them creatively.