The index finger (forefinger), the finger between the thumb and middle finger, commonly used for pointing.
人差し指で画面をタップしてアプリを開いた。
I tapped the screen with my index finger and opened the app.
彼女は人差し指に小さな火傷の跡がある。
She has a small burn mark on her index finger.
矢印のところを人差し指で指してください。
Please point with your index finger at the arrow.
Occasionally used to refer to the second toe (the toe next to the big toe).
水ぶくれは人差し指の部分にできていた（足の）。
The blister appeared on the second toe (the one next to the big toe).
医者は彼の人差し指（足）を念入りに調べた。
The doctor carefully examined his second toe.