It's simply an inflammation of the tendons on the inside of the front of the lower leg. Generally, shin splints are caused by too much stress on the tendons, due to tired or stiff calf muscles. Athletes are often prone to shin splints, which can be aggravated by running on hard surfaces, such as concrete.
Symptoms can include pain along the shin, especially to the touch.
The pain is usually most severe at the beginning of a run, but may dissipate as the muscles warm up. The pain will ordinarily return after the running stops. In order to prevent shin splints, it's important to stretch properly before exercising. Walking on your heels and flexing the ankles stretches and strengthens the tendons in the front of the lower leg. Practice picking up small objects with your toes to strengthen the arches of your feet.