The male version of "camel toe". Where said male's pants are so tight and/or transparent, the shape/details of their anatomy are clearly visible even through the garment, resembling the appearance of a moose's lower ankle (or "knuckle").
"When I watched wrestling last night, that tag team had on spandex shorts SO tight, they were sporting some SERIOUS moose knuckle!!!"
When a male is wearing clothing or underwear so tight to his genital area, the testicles and/or penis are pushed into the shape resembling a moose knuckle.
