Cascading reels is a gambling term most often used by slot machine and video slot players. The term describes a bonus feature that appears each time you land a winning combination.
Video slot software developers have designed numerous creative cascading reels. However, one thing that they all have in common is that the feature is triggered only after landing a winning combination. The symbols that were part of the winning combination then disappear from the reels and are replaced by a new set of symbols, allowing you to win again.
Think of it as a slightly modified re-spin feature.
Furthermore, the feature can trigger itself, meaning it will keep being triggered as long as you are landing winning combinations after each new cascade. In some cases, cascading wins are accompanied by a multiplier, which makes each subsequent win more lucrative than the previous one.