It's an ingredient used in Alchemy that can be obtained through farming in a garden rarely. Mostly from herbs or mashrooms. You can buy them in the market, too.

you can get them via wild herb gathering with a hoe you can get them via farming, if you grow the right seed, it also possible to get mysterious seed that have a 100% chance of getting Fruit you can buy them from the central market they are mainly used in alchemy and othere various lifeskill activity