Packing
From the Hudson’s Guide
The term “packing” refers to the process of creating a male-looking and/or male-feeling bulge in one’s crotch. This can be accomplished through a home-made or store-bought pants stuffer, or through a realistic-looking prosthetic device. A packing device may be referred to as a “packer” or “packy,” or as an “STP packer” if it can also be used to pee through while standing up (STP= Stand To Pee). Some guys simply refer to their packer or prosthetic as a cock and balls, a dick, etc.
To read more, please visit http://www.ftmguide.org/packing.html