The letters P – I – M – A represent the fingers of the strumming hand. 

P = thumb, i = index, m = middle and a = ring. (see illustration)

Original labels are in Spanish: 

dedos = pulgar, indicio, media y anular. 

The left (or fretting hand) fingers are indicated by numbers 1, 2, 3, and 4, respectively index, middle, ring and little finger. Complex classical guitar music is often fingered for both right and left hands.

Flamenco guitarists, who employ the little finger for strumming, represent it with the letter C, mainly for rasqueado rhythmic strumming patterns.