As with peah (the corner of a field) and leket (the gleanings), we have two mitzvos regarding olelos, the portion of a vineyard that must be left for the poor. The previous mitzvah described the obligation to leave olelos, while this mitzvah details the prohibition against picking the vineyard clean.
So, what exactly are olelos? There’s some difference of opinion there. The Rambam (Maimonides) says that the term refers to small, individual bunches of grapes, while Ramban (Nachmanides) maintained that olelos means small, underformed grapes. In any event, one is obligated to leave an unharvested portion of his vineyard, corresponding to the unharvested fruit of an orchard. (See Deuteronomy 24:20-21 and Talmud Chulin 131a.)
If the entire vineyard is made up of olelos, the poor get the whole thing. As with peah, if a person forgot and accidentally cleared his vineyard, he must make up for doing so by giving the appropriate portion of grapes to the poor.
This prohibition applies to both men and women but only in Israel. It is discussed in the seventh chapter of tractate Peah in the Mishnah and is codified in the Shulchan Aruch in Yoreh De’ah 332. It is #212 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #8 of the 26 mitzvos that can only be performed in Israel according to the Steipler Gaon.