The act of placing the head of ones penis inside the foreskin of the partner's penis.
"Me and Miley Cyrus practise a lot of space docking cuz she has a large cheezy foreskin " ( as my aunt would say : "sometimes i dont have time to take a bath, so my dick smells like cheese" )
As well as referring to the act of placing the head of an erect penis inside the foreskin/meatus of another erect penis, docking also denotes the act of placing an unerect or flaccid penis along the length of an exposed buttock crack. In this act (often performed in British, public, boarding schools), erections are very much frowned upon.
Eddie bent over, exposing his bumhole with a neatly parted cheek, as Tony docked him expertly. "Oh what a beautiful docking", exclaimed Lara.