Tertiary (late) stage syphilitic sores on the vaginal wall (i.e., cunt). The lesions are red with a necrotic and oozing center. These sores are typically the sign of a long term syphilis infection and the implication is that if you suffer from them, you are sexually promiscuous (and nasty).
That girl is so skanky, I bet she has a gumma cunt." Can also be used to as an embellished derogatory name, e.g., "she is such a gumma cunt."
by Evelyn Waugh April 09, 2011