Original: Speeds where only some parts of the air around an object (such as the ends of rotor blades) reach supersonic speeds are labeled transonic (typically somewhere between Mach 0.8 and Mach 1.2).
Simplified: Speeds where only some parts of the air around an object (such as the ends of rotor blades) reach supersonic speeds are called transonic (typically somewhere between Mach 0.8 and Mach 1.2).