What does R.M. Hare mean by ought?

In general, the philosophical distinction between “is” and “ought” is between statements of plain fact, such as “the apple is red”, and statements that endorse a course of action, such as “you should eat that apple”. For R.M. Hare, moral statements –the ones that that belong in the “ought” category –needed to be accompanied by action. In other words if I say “I ought to give money to the poor” then that statement should be accompanied by my actually giving money to the poor.

Hare’s “oughts” are closely related to Immanuel Kant’s “categorical imperative”, which is the idea that a moral rule is a rule that I believe should be true universally, a rule that would make the world a better place if everyone followed it (including myself).

I hope this helps. I am far from being an expert on Hare, but there is a good article on him on Wikipedia: http://en.wikipedia.org/wiki/R._M._Hare.