Short for 'Nipple Show Through', when a woman's nipples show through her shirt, blouse, bra, bikini etc.
'My wife took me to that
lingerie fashion show last week. She wished she hadn't
in the end. Even where we were sitting, I could see the NST on the models! I think she realised I was
drooling.
'Hey, look at the NST on the chick
in the pink T-shirt.'
'You missed it mate, she got out of
the pool, and man,
the white bikini, and, wow, the NST.'