The 123rd mitzvah is that we are commanded to leave over for the poor those [poor-quality1] grape clusters which are normally2 left in the vineyard during the harvesting process. These are called olelos.
The same verse,3 "You must leave them for the poor and the stranger," also refers to this mitzvah, since it follows mention of olelos.
The details of this mitzvah are explained in tractate Pe'ah.
The Biblical prohibition applies only in Eretz Yisroel.4
