The finger next to the thumb, used for pointing or indicating.
I pointed at the location on the map with my index finger.
He raised his index finger to signal for silence.
second toe
The toe next to the big toe; sometimes called the index toe. Less common than the finger sense.
I got a blister on my second toe.
He pointed at a spot on the map with his index finger.
The teacher held up her index finger and said, "Wait a moment."