Herm is when a plant produces male parts (balls) and female parts and pollinates itself and possibly others nearby. The male sacs on a (herm) will likely will carry the “herm” characteristics to itself and any other plant it pollinates.
Herm can happen from stress, environment, light leaks, bad genetics (herm plants produce herm seeds) (you buy/grow herm seeds unknowingly). It pays off to dive into breeders local and aboard. Find good genetics.
Nanners look like tiny bananas that sometimes protrude through a bud or sometimes stay inside a bud. and are female only pollen and not herm. Since nanners lack the males Y chromosome nanners produce fem seeds and don’t pass on herm traits.
Nanners is a way fem plants try to preserve its genetics. Clones are less likely to nanner and are more stable.