This is a labeling system found on music notation and tablature that indicates which picking hand fingers should be used to pluck the strings. The PIMA system uses the symbols p, i, m, a, and occasionally c to direct the performer to use a specific finger to pick each note for the part.
p = pulgar (thumb)
i = indice (index finger)
m = medio (middle finger)
a = anular (ring finger)
c = chicito (little finger) sometimes labeled “e” or “mignolo”