Penny, The men wear lots of short sleeve silk shirts on casual night, too. I don't think I saw too many suits on informal night. To answer your question, casual is no jacket or tie and informal is a jacket, tie optional.
🚢 Cruise with your favorite Keene Luxury Travel Staff Member! 💰 5% KLT Reward plus Shipboard Credit available (amount varies per voyage)! 💲 Offering Enhanced KLT Rewards on voyages hosted by Ngaire & Clay!