Averaging down means buying more of something that has dropped, to lower your average cost. Done with a plan, it is how good positions get built. Done out of hope, it is how accounts get wrecked.
The dangerous version is catching a falling knife: adding again and again into a price that keeps falling, just to feel better about being underwater. Each buy lowers your average a little, but the position keeps growing and the loss keeps growing with it.
The smart version has rules you set in advance. You only add if the asset is still something you want to own, only at levels you planned before the drop, and only with capital you set aside for it. If the reason you bought is broken, you do not add. You get out.
Averaging down is smart only when it is planned and the thesis still holds. Adding just because it is cheaper, with no plan, is catching a falling knife.
Tip. Ask one honest question before adding to a loser: would I buy this today if I owned none of it? If the answer is no, do not average down. You are hoping, not investing.