Definition

Fat Upper Ass Area—that distinctive little pocket of fat some people get at the small of their back (where a tramp stamp would go), usually only visible in summer when everyone's showing more skin. It's apparently hereditary and oddly polarizing among friend groups.

Example Usage

Everyone was pointing out their FUAAs at the beach last summer; apparently it runs in families.

Source: Urban Dictionary (https://www.urbandictionary.com/define.php?term=FUAA&defid=2780052)