Those not sticking to strict code standard are taken to a stern deck and beaten severly with a rubber hose. I the off chance that this is not happening, you will find that for "casual" shorts and jeans are not appropriate for the evening meal in the dining room. The semi formal is what other lines call "smart casual". Celebrity suggests a sport jacket for men. You will find many without that. Formal would generally mean tux or dark suit for men. You will find many in not more than a sports coat and a few in only a dress shirt.