A Puss filled growth on the outer genetalia. Typically drained accidentally during masterbation, as you won't be having sex with a fatty corpusle on you unit. The drainage will often cause the spread to the lower genitalia, or the scrotum. Often these are called carbuncles. (see defintion of carbuncle)
When you think you have herpes, you probably do. Now don't pop that fatty corpusle.