Back-and-fill definition

Price action, for a stock or other financial instrument, that isn’t indicative of a substantial trend; prices remain in a narrow range. Prices rise, but then fall back, filling in the space on a price chart inside a larger price movement.

(nautical) To manage the sails of a ship so that the wind strikes them alternately in front and behind, in order to keep the ship in the middle of a river or channel while the current or tide carries the vessel against the wind.