Inadequate mating material
Inadequate mating material is a chess rule whereby one player does not have enough pieces to checkmate the other player. If neither player has enough mating material then the game is a draw. A typical example is “Kings only” which is a draw as neither player can do anything.
The official designation of inadequate mating material is very limited. If a player has a pawn, even if it’s blocked up, that player still in theory has mating material because the pawn could be queened. Similarly, if a player has a Rook or a Queen, that is definitely adequate mating material.
Inadequate mating material therefore only applies to positions without pawns, and with only the King plus Knights and Bishops. The simplest case is “King vs King” which is drawn. Other draws are “King plus Bishop vs King” and “King plus Knight vs King”. Positions with two minor pieces, or one minor piece for each player, are subject to more obscure rules.
Some tournaments use inadequate mating material in regard to chess clock time forfeits. If you win on time, but you have only a King, you might still only get a draw by the tournament rules because you don’t have mating material.