14 CFR 437.3: Definitions.

Envelope expansion means any portion of a flight where planned operations will subject a reusable suborbital vehicle to the effects of altitude, velocity, acceleration, or burn duration that exceed a level or duration successfully verified during an earlier flight.

Exclusion area means an area, within an operating area, that a reusable suborbital vehicle's instantaneous impact point may not traverse.

Operating area means a three-dimensional region where permitted flights may take place.

Permitted vehicle means a reusable suborbital rocket or a reusable launch vehicle that will be launched into a suborbital trajectory or reentered that is operated by a launch or reentry operator under an experimental permit.

Reentry impact point means the location of a reusable suborbital vehicle's instantaneous impact point during its unpowered exoatmospheric suborbital flight.