I believe that (almost) everybody things "ought" means the same thing, and that people disagree about the concept that "ought" usually refers to.

What is the difference between what "ought" means and what it refers to?

Edit:

This concept is special because it has a reverse definition. Normally a word is defined by the situations in which you can infer that a statement about that word is true. However, "ought" is defined the other way - by what you can do when you infer that a statement about "ought" is true.

In the above, do you say that "You ought to do X." is exactly equivalent to the command"Do X!", and "I ought to do X." means "I will do X on the first opportunity and not by accident." ?

Is it the case that Katy ought to buy a car? Well, I don't know. But I know that if Katy is rational, and she becomes convinced that she ought to buy a car, then she will buy a car.

Ought we base the definition of "ought" on a pretty complicated notion of rationality?