A UI is intuitive when users understand its behavior and effect without use of reason, experimentation, assistance, or special training.
For such intuition to be possible requires prior knowledge, either from experience in the real world or with other software. So, for example, if something looks like a push button, we know from the real world that we can click on it to make something happen. Alternatively, if something looks like a link, we know we click on it from experience with other software.
We can boil this definition down to two requirements: affordance and consistency, where affordance allows us to predict what is going to happen based on appearance, and consistency to make that prediction correct. Labeling and context are also factors in making the prediction.
So is intuitive just a fancy word for affordance, consistency, and predictability? It could be, but when people use the term, I think they have more in mind.