A theoretical draw is a chess position in which, no matter how both players continue, the game cannot end in checkmate: it will inevitably result in a draw with perfect play from both sides.
This concept applies primarily to endgames. A position is called "theoretically drawn" when the remaining material is insufficient to force checkmate, or when the defending side has precise defensive resources available — such as a fortress, perpetual check, or a forced stalemate — that prevent any loss. Classic examples include king and bishop versus king alone, or king and knight versus king alone: the stronger side simply cannot force checkmate. Similarly, the Philidor position in a rook-and-pawn versus rook endgame is a theoretical draw when the defender knows and applies it correctly.
In practice, recognizing a theoretical draw is just as important as looking for a win. If you are at a material disadvantage, identifying that the position is theoretically drawn gives you a clear, achievable goal: steer the game toward that safe zone. Conversely, if you hold the advantage, knowing that certain exchanges lead to a theoretical draw will prevent you from simplifying by mistake and throwing away a winning advantage.