Final answer:
The correct answer for a definition that BEST describes genu varum is option C, which describes a condition where the angle between the femur neck and shaft is less than 125 degrees.
Step-by-step explanation:
The definition that BEST describes genu varum is C. Genu varum, also known as bow legs, is a condition where there is a deformity with the legs curving outward.
This condition can be characterized by the angle between the femur neck and shaft being less than the normal 125 degrees, leading to an appearance where the knees stay apart when the individual stands with their feet together.