To shuttle is to transport. Via any method or vehicle. You can put wheels ( or a rocket engine) on a box and call it a shuttle. Last time I checked they weren't putting SRB's on the buses though.
Have a quick glance at Blazer's quote in my signature.
Also, you get 3 levels of efficiency.
1) SSTO. Efficiency sucks. But easily reusable.
2) Space Shuttle. Efficiency sucks, but nowhere near as much as an SSTO due to boosting, thus you can get a bigger payload to orbit for a much higher payload to launch mass ratio. Reuse takes work but can be done. Requires actual engineering either way.
3) Rocket. Very efficient in terms of payload to launch mass, and even more so if not reused.
Thus an SSTO and a Space Shuttle has a clear distinction from one another.