In mechanical engineering, an envelope is a solid representing all positions which may be occupied by an object during its normal range of motion.
Minimum and maximum tire inflation pressures and wear conditions may also be considered when generating the envelope.
The results of this analysis tell the engineers whether that wheel/tire combo will strike the housing and components under normal driving conditions.
Of course, high speed collisions, during an accident, are not considered "normal driving conditions", so the wheel and tire may very well contact other parts of the vehicle at that time.
Some factors of a robot's design (configurations, axes or degrees of freedom) influence its working envelope.