The terms "inversion" and "eversion" are used to describe the movements of the foot. "Inversion" is the movement in which the sole of the foot turns inward relative to the lower leg. "Eversion" is the movement in which the sole of the foot turns outward.
Example
An example of the use of these terms is when someone twists an ankle, with the foot rolling inward. This is called an inversion injury. This can lead to damage of the ligaments on the outside of the ankle.
Eversion injuries are much less common because the mobility of the foot outward is not as great.
These terms are mainly used by (para)medical professionals, such as physicians and physical therapists, to communicate more precisely about the location of an injury or problem. As a patient, you do not necessarily need to be familiar with these terms, but they can help you better understand a medical report.