**Core Concept**
Inversion of the foot refers to the movement of the foot where the sole turns toward the midline of the body, resulting in the plantar surface moving medially. This is a key concept in foot biomechanics and gait analysis, involving the orientation of the tarsal bones and the position of the foot relative to the body.

**Why the Correct Answer is Right**
During inversion, the foot rotates so that the sole faces inward, toward the medial (inner) side of the body. This movement occurs primarily at the talocrural and subtalar joints, with the talus and calcaneus moving medially. The medial border of the foot (the inner edge) becomes more vertical, and the sole rotates inward, aligning the plantar surface with the midline. This is the anatomical definition of inversion.

**Why Each Wrong Option is Incorrect**
Option A: The sole does not face upwards; that would describe dorsiflexion, not inversion.
Option B: Facing downwards would describe plantar flexion, not inversion.
Option C: Lateral movement is eversion, not inversion.

**Clinical Pearl / High-Yield Fact**
Remember: **"Inversion = inward rotation of sole → medial"**. Inversion is the opposite of eversion (which turns the sole outward). This is crucial in diagnosing foot injuries, such as ankle sprains, where inversion causes ligamentous strain.

✓ Correct Answer: D. Medially