Little finger

The little finger is the most ulnar and usually smallest finger of the human hand, opposite the thumb, next to the ring finger. It is also called the fifth finger, digitus minimus, digitus quintus, or digitus V in anatomy, and colloquially called the pinky finger.

A pinky promise (also known as a pinky swear) is when two people wrap their pinky fingers around the other person's pinky and makes a promise. Traditionally, it's considered binding and the person who breaks the promise must cut off their pinky finger.