Finger numbering

The first finger is an ambiguous term in the English language due to two competing finger numbering systems that can be used. It might refer to either the thumb or the index finger, depending on the context. The second finger is another ambiguous term in English. It might refer to either the index finger or the middle finger, also dependent on context. The same can be said for the third finger (referring to either the middle finger or the ring finger); and the fourth finger (referencing either the ring finger or the pinky). The fifth finger will exclusively refer to the pinky, (also called the little finger).

Finger numbering systems
The ordinal numbers of the fingers of the human hand are numbered ambiguously in the English language. This is due to two competing finger numbering systems that can be used. For instance, the first finger might refer to either the thumb or the index finger, depending on the context.

Five-finger system
In the Five-finger system, the first finger usually refers to the thumb (or first digit) in a medical context, or in a musical context when referring to playing keyboard instruments, such as the piano or accordion.

The second finger under this system will refer to the index finger (or second digit) in medicine, or in a musical context when referencing the playing of keyboard instruments.

The third finger usually refers to the middle finger (or third digit) in a medical context, or in a musical context when referring to keyboard instruments.

The fourth finger refers to the ring finger (or fourth digit) in a medical context, or in a musical context when referring to keyboard instruments.

The fifth finger refers to the pinky finger (or fifth digit) in a medical context, or in a musical context when referring to keyboard instruments.

Four-finger system
Here, in the four-finger system, as well as in common English, the first finger refers to the index finger (the finger next to the thumb). This designation carries over in a musical context when referencing the playing of stringed instruments (such as the guitar), woodwind instruments (such as flutes, pipes, or piccolos), and brass instruments (such as horns).

The second finger refers to the middle finger in common English, or when playing string, brass, or woodwind instruments in music.

The third finger refers to the ring finger in common English,  or in a musical context when referring to string, brass, or woodwind instruments.

The fourth finger refers to the pinky (or little) finger in common English, or in a musical context when referring to string, brass, or woodwind instruments.