The lateral head is the outer head of the two gastrocnemius muscle heads. The gastrocnemius is the muscle located to rear of the lower leg and comprises the main bulk of the calf.
The gastrocnemius is recruited during the extension of the ankle when there is no significant bend in the knee. The muscle is highly active during the eccentric (lowering) portion of a calf raise, so it is important to perform the eccentric phrase in a controlled manner.
There is a common belief, particularly among the bodybuilders, that pointing the toes inward during the calf raise will target the lateral head and pointing the toes outward will target the medial head. This is only half true – research by Dr Per Tesch has shown that pointing the toes outward does indeed increase medial head activity, but pointing the toes inward does not cause greater activity in the lateral head.