This is when the mouth is wide open awaiting a deposit.
Usually a woman, awaiting a man's seamen.
This position is also used for skull fucking (gag or throat fucking) where a man shoves his penis down a the woman's throat until she gags or even throws up.
It is also used for cum swapping.
The perfect position for the woman is to lay sideways on the bed, with your head off the edge and the neck right on the edge of the mattress with your mouth wide open awaiting his deposit.