What is the true meaning of OOP?

Enlighten me, what is the true essence of OOP? Is is just the use of objects and classes, or is it something more?

and is OOP really better than structured programming?

Objects are about maintaining their own internal state, not being "smart", not inheritence, not classes, not interfaces, not instances, not singletons, not replacable, and especially not Java, like Sun would try have you believe.