Again, I did NOT say that casual on a cruise ship means a jacket and tie. I said that the origin of the "casual" dress is an affair which is not formal (black tie), or informal (business suit). This is what it has meant on the past and what it basically means now in strict circles.
But I also said that a cruise ship is different, both because they redefine the word for themselves AND because people who don't know what a classic dress code even is have redefined it. To 90%+ people, casual means AT MOST dockers and a polo shirt. And that's fine - I'm not criticising that. That's what I do for casual (except I despise polo shirts, so I wear a button down). I'm simply saying that if one wants to get into a TECHNICAL or SEMANTIC arguement about what "casual" really means in the dress code sense, as someone did, then the cruise lines an common populace has it wrong, as a jacket/blazer is technically part of a casual outfit.
formal = black tie
informal = dark suit
casual = jacket (like a blazer over your dockers and polo shirt), no tie required, but it can be acceptable for some situations.
Everything else is less than casual.
This is from technical sense, not a cruise ship or party-at-home sense. It's for informational purposes, and I'm not telling anyone they have to wear a jacket to dinner on a cruise ship.