Packer
The packer is a padding or a phallic-shaped object positioned in the underwear or between it and the pants to simulate the presence of the penis; it is a common practice for trans guys, both during and after passing.
The function of the packer is to create volume in the genital area, which would otherwise be empty, therefore female.
The shape of the packer can be approximate, therefore aimed at creating the correct form, or phallic shape, often equipped with a scrotal / testicle pouch.
This practice called ‘packing’; the name derives from the first materials used to build the packers: pieces of fabric.