Opposite of
机构 (jīgòu, institutional investors). Related slang:
韭菜 (jiǔcài, 'leeks') for retail investors who keep getting 'harvested' by market crashes and rebuy;
大户 (dàhù) = big individual investors;
中户 (zhōnghù) = medium ones. Being
散户 means you're small, retail, and usually last-to-know.