What, if any, would be the most correct term for the aerodynamic flight control surfaces of SpaceX's Starship?
As far as I know, the only other example of this flight profile in aviation is post-stall maneuvering, especially for flat spin recovery. For planes, control in these flight regimes is mainly accomplished by thrust vectoring and canard/stabilator actuation. The Starship flaps don’t match these.
Another close sibling of this flight profile is the Shuttle reentry. The Shuttle used a body flap as well as conventional Delta-wing control surfaces in combination with RCS to maintain a specific, high AoA during hypersonic reentry, then transitioned to gliding for approach and landing. The Shuttle body flap (under the engines) has the closest resemblance to the Starship flaps out of any space vehicle I know. It has a much smaller actuation range, though.
Of course, the control surface naming depends on how you define the vehicle frame; with thrust direction-forward, the flaps are variable-dihedral. With velocity direction-forward, the flaps are variable-AoA with a wide actuation range.
The noun I would go with would be variable-drag flaps. Spoilers aren’t correct; there isn’t another airfoil to spoil. Airbrakes usually don’t contribute to attitude control.