Tunnel vision in chess refers to a cognitive bias where a player becomes overly focused on a specific area of the board, a particular plan, or a single piece, often at the expense of considering the broader position and other potential threats or opportunities. This narrow focus can lead to missing important moves, tactics, or strategic considerations, ultimately resulting in suboptimal play or even blunders. It's crucial for chess players to maintain a wide scope of attention, continually reassessing the entire board to avoid tunnel vision and make well-rounded decisions.