An outpost is a stable square — typically in the center or enemy territory — where a piece, most often a knight, can be permanently stationed without being driven away by an opponent’s pawn. It is generally located in the opponent’s half of the board or in the center, and no enemy pawn can attack it.
For a square to qualify as an outpost, two conditions must be met: no enemy pawn can attack it (because the neighboring enemy pawns have been traded away, are absent, or are fixed), and a friendly piece can be maintained there stably. For instance, if Black’s pawns on the c- and e-files have been exchanged or are immobilized, the d5 square becomes a natural outpost for a White knight. Installed there, the knight controls a wide range of key squares and disrupts the coordination of Black’s pieces.
In practice, look for squares that your opponent’s pawns can no longer guard due to their pawn structure — these are natural outpost candidates. Plan your moves to place a knight on such a square, and support it with a pawn or another piece so it remains entrenched for as long as possible.