Well THERE'S the pot calling the kettle black!
As I say over and over again on this forum, there is a DIFFERENCE between the formal rules of dress and the common usage of these terms. Someone was offering a semantic arguement about what casual means and I pointed out that technically (by the formal rules), it means a jacket. NOW, not the 1950's.
But I also point out that to most people in most situations, casual means something less than that. On a cruise ship, for example, that's what you will see.
So ultimately the answer is, yes there is a formal deffinition to all of these dress codes, but MOST people in MOST situations use whatever the current common usage is and also tend, whenever possible, to push even further away from the "Formal" end of the scale. That's why you see people in dockers on Formal nights. And why others, should they want to do so, get away with it as well. So wear what you want, no matter what you do, you will have company. But having company doesn't make you right.