Normal
I'm sure you will get no end of opinions on this subject and here is mine. Formal is suit and tie at minimum, although a tuxedo is preferred. With that said, you will see all sorts of interpretations on this theme and I doubt the cruise line will enforce formal requested, suggested, recommended or however they phrase it in their guidelines. We enjoy dressing for dinner and I would like everyone else to as well, but I understand and accept that not all my fellow vacationers share this point of view. By the way this doesn't mean my evening is ruined spoiled or otherwise less enjoyable because some people don't subscribe to my "Grand vision" of formal dining.