A pimple was a small deformity found on a Humanoid's skin and was a result of blockage of a pore.
The Klingon equivalent of a pimple was the gorch. (Star Trek: Insurrection)
In 2366, Q contemplated, after being transformed into a Human by the Q Continuum as punishment, on the possiblility of having a pimple. (TNG: "Deja Q")
Lwaxana Troi once said that making young boys reasonable often gave them pimples. (TNG: "Cost of Living")
The Doctor, shortly after his activation, complained in 2371 to Kes in sickbay that every "runny nose, stubbed toe, pimple on a cheek" was his responsibility. (VOY: "Parallax")