What are Expanding Wilds ?

The name speaks for itself. Expanding wilds are single substituting symbol that expand to fill a whole reel whenever they appear. If the Wild symbol lands on the payline, it expands vertically or horizontally. As a consequence, a single Wild symbol replaces all symbols on a given reel into Wild ones. Expanding Wilds can drastically increase your winning combinations. Expanding Wilds can be found for example at Sparks slot from NetEnt.