Define Flat-chested Meaning

having little or no female breast development

a women without boobs

A girl with absolutely no boobs who often likes to pack her bra to make it seem different

When a girl's chest is flatter than a board of wood

A woman/girl with very small or no breasts. Usually seen as a curse but some people like the lack of boobs.

(1) a female's upper torso with no or little curvature, having no or very small breasts;
(2) a female with such a chest, or more regularly, who is thought to have a flat chest, but actually just has A or B cups.
Usually meant as an insult or self-deprecating remark, but reclaimed by some as a source of pride and self-worth.

some one who is a part of the "ITTY BITTY TITTY COMITTIY"
in other words, very small breasts.
boobless.

A girl with no boobs. It’s pretty bad when her ribcage sticks out farther than her boobs.

When one is extremely sexually attracted to a girl with a Flat Chest.

The term was coined from the AnimeOverlord when Ainz Ooal Gown was trying to comfort the flat chested character on the show, Shaltear Bloodfallen who was trying to fake having Big Breasts to impress him.

A girl that is so flat chested that she is often mistaken for a guy.