seatbelt boob; breast bisected by strap
Slang term describing the visual effect when a strap (seatbelt, bag, etc.) presses between a woman's breasts, making them appear separated. Often used in otaku and online communities.
I can't help but notice her seatbelt boob.
I like drawing the breast-bisected-by-strap look in my illustrations.
Wasei-eigo (Japanese-made English) from 'pie' (slang for breasts) + 'slash', referring to the diagonal line created by a strap across the chest.