The 212th prohibition is that we are forbidden from completely harvesting a vineyard.
The source of this commandment is G‑d's statement,1 "Do not pick the olelos in your vineyard." You must instead leave them for the poor.2
This law does not apply to other trees, even though they are similar to grapevines. The prohibition,3 "When you beat the fruit from your olive tree, do not go back over it" [is not related to this mitzvah of olelos but] is part of the prohibition against taking shik'cho (forgotten produce).4 From this verse which prohibits taking shik'cho from olive trees we learn that shik'cho applies to all trees. [The law of olelos, however, only applies to grapes.]
This mitzvah is also in the category of lav shenitak l'aseh (a prohibition with a remedial positive commandment).
The details of this mitzvah are explained in tractate Pe'ah.5
