Used to refer to younger females, typically 18 to 22 years old, who possess trim or tight midriffs. Largely due to them not having had the time to get fat.
The term is generally used in a fishing vernacular, as the target group usually travel in packs, or schools - like fish, and tend to still be going to school.
Not to be confused with jailbait, which is the correct term for an undersize hardbelly.
Mick: Hey Jack! You should have gone to the 21st last night.
Jack: Nah, I'm too old for that shit.
Mick: I snared myself a real nice hardbelly. Had to throw the rest back because they were undersize.
Jack: Next time you get invited to a 21st, YOU RING ME.
A sexy young teenage girl with a natural flat smooth tummy that hasn't had her body ruined by pregnancy or over indulgence. Not to be confused with a hardbody that requires work outs and usually refers to a male.
Sam: Hey check out that gorgeous little hardbelly. Fred: Careful buddy.....15 will get you 20.