Gear' technically means an equipment or apparatus used for a particular purpose. Wheels are just a part of the complete Landing Gear. It is technically called the Undercarriage. The wheels, along with the strut, fairings, truss tube, brake assembly form the landing gear or the undercarriage. read more
Wheels are not called landing gear they are called wheels only. Wheels are a part of landing gear. For a layman the wheels are the recognizable part of landing gear so when they say "the landing gear is retracted" they mean the whole landing gear but to us we only recognize the wheels hence the confusion. read more