Ruth is collecting left-over barley at harvest time in order to provide for herself and Naomi, her mother-in-law, with whom she lived in Bethlehem.
Gleaning is the act of collecting leftover crops from farmers’ fields after they have been harvested.
According to the of the Torah, farmers should leave the corners of their fields unharvested, and they should not attempt to pick up that which was dropped or harvest any left-overs that had been forgotten when they had harvested the majority of a field. These things should be left for the poor, for strangers, widows, and orphans.