noun. An assticular bonanza. Or, simply the buttockial region.
Real citation: “The blood spatter stuff will be very easy as it is one shot, or a pain in the buttanza as it has blood effects.”(Jack Daniel Stanley, Sept. 13, 2006, http://www.dvxuser.com/V6/archive/index.php/t-65228-p-2.html)
Made-up citation: "The military calls the buttanza the fourth point of contact; I just call it sweet merciful ass."