A "locked reel" in slot play refers to a situation where one or more reels on a slot machine do not rotate during a spin, typically due to special features or game mechanics. This can occur in bonus rounds or when a specific triggering pattern aligns, allowing certain reels to remain fixed while others spin. The concept adds an element of excitement and potential for increased winnings by enhancing the chances of landing winning combinations with the locked reels while the others continue to spin.