Kev's explanation was very well stated. Smooth just means you're not choppy with anything you do on the bike.
We train for this all the time, focusing on every aspect, one at a time.
Throttle control is the most boring so we do that first. Gently on the throttle and gently off, on and off, over and over again until all of the choppiness is gone. We practice it slowly but that doesn't mean that smooth=slow. Smooth can be done fast just as well. What you're shooting for is extreme control. Nothing ever gets done suddenly or without warning. Throttle control on the Busa is VERY difficult to master.
Brakes, same thing. Gradually on, gradually off. Just as you don't ever slam the brakes all of a sudden, you don't ever let off the brakes suddenly either. Again, the question is about control. Gradually apply, the gradually release, rear brake just a split instant before the front brake. The front brake, you want to be using the tips of your fingers on the brake lever. Squeeze gently. Again, in the partking lots, you practice over and over and over again until boredom sets in. Then do it again in a coupla three weeks. It becomes habitual to be smooth on your control of the brakes.
The other controls, practice smoothness with all of them. Practice is done slowly and gradually. In real life, it can be done very quickly and retain smoothness.
Turns, same thing. Practice for a smooth, balanced line.
Learn to be loose on the bike. It doesn't really need you to hold it up. It can ride itself juuuuuuust fine. Bikes have most of their problems because of their rider!
It takes practice and most of the things we all need to learn CANNOT be learned while out riding. They MUST be learned in a sterile (parking lot) environment with little or not interference.
Just some thoughts. Any elaboration, you know me. I'll type to your heart's content!
--Wag--