When a woman milkstamps someone and she lactates while doing so. This is regardless of whether it is a skim, 2%, 1/2 and 1/2, or whole milkstamp. It is also considered a wet milkstamp even if the breastmilk doesn't get on the milkstampee.
When a woman milkstamps someone while she is wearing a shirt or torso covering clothing but is not wearing a bra or any other brassiere like mammary restraint.