Hefting is a night-time sport played in dormitories and other communal sleeping places (tents, hostels, etc.). Once the lights are out, a player leves their own bed to attack another person by wrestling the victim (Heftee) on their bed; whoever is on-top when the lights are switched on wins. Due to this, a Heft must be conducted when the lights are out. If the Heftee ends up on-top, they win the Heft.
A Flying Heft is conducted by jumping from a top bunk-bed straight onto a heftees bed.
An Owen is a mis-Heft caused by two or more people simultaneously attempting to Heft another whilst, unbeknownst due to the darkness, that person is already Hefting someone else, and the two luckless Hefters end up unwittingly Hefting each other insead.
* These videos are coming directly from Youtube, they may or may not be most relevant to the word "Heft"