The little finger, also known as the fifth digit or pinky, is the most ulnar and usually smallest finger of the human hand, opposite the thumb, and next to the ring finger.
The word "pinky" is derived from the Dutch word pink, meaning "little finger". In some places "pinky" is also a traditional name for the smallest (youngest) child in a family (especially, when father and mother have 3 children).
Among American children a "pinky swear" (or "pinky promise") is made when a person wraps one of their pinky fingers around the other person's pinky and makes a promise. Traditionally, it's considered binding, and the idea was originally that the person who breaks the promise must cut off their pinky finger.
The Red String of Fate is a belief originating from Chinese legend. According to this myth, the gods tie an invisible red cord around the ankles of those that are destined to meet one another in a certain situation or help each other in a certain way. Often, in Japanese culture, it is thought to be tied around the pinky.