A feature where the physical size of the game grid (reels or rows) actually gets bigger, usually during a bonus round.

Reel Expansion is a feature where the physical size of the game grid (reels or rows) actually gets bigger, typically upon entering a bonus round like free spins.

This goes beyond simply adding a multiplier; it aims to expand the 'board' of the game itself, providing players with a wider field of opportunity and fundamentally increasing the number of winning ways.