What does Birmingham belly-flop mean?

Birmingham belly-flop meaning in Urban Dictionary

a derivative regarding the "Alabama jackhammer"; a standing "69" where woman is upside-down performing fellatio. Once the guy senses the nearing regarding the climax he carries out an Alabama jackhammer like maneuver in which he belly-flops (nevertheless within the 69 position) on the bed/floor/table, etc., and slams his penis into the straight back of woman's neck releasing a heap of semen into the bronchial tubes or esophagus associated with girl