The term "falling reels" refers to a special in-game principle used by some online slots. In cascading reel slots, symbols fall down onto the screen from above, usually from the rows above. When you land a winning combo, the symbols involved disappear and are replaced by new ones falling from above. This allows you to land multiple wins on a single spin as long as you get one or more winning combos. This is a particularly exciting and entertaining gameplay function that can find at Jackpot.de and affiliate sites.