An outpost in chess is an advanced square—usually on the fourth, fifth, or sixth rank in the opponent's territory—that is defended by your own pawn and cannot be attacked or driven away by an enemy pawn.
Here, the c6 square that the knight occupies is a great outpost square. The knight can’t be moved and it is really cramping anything black would like to do. Black is currently up in material but white has a better game because of the knight on c6. A great outposts can change a game from even to a decisive win. Make sure you understand how to recognize a good outpost square in your chess game
An outpost is a square where you can keep a piece where your opponent can’t capture the piece without giving up a material advantage. Outposts can be one of the most important strategies in a chess game as it allows you to have a huge spacial advantage and puts constant pressure on your opponent’s position.
The Best Pieces for Outposts::
Knights: Knights are short-range pieces that love secure, central nests. A knight on an outpost (like d5 or e5) becomes an absolute monster because it cannot be kicked away by a pawn and hits surrounding squares effortlessly.
Bishops, Rooks, or Queens: While less common because higher-value pieces are more vulnerable to minor trades, placing a rook or queen on an advanced outpost can completely paralyze an opponent's position.
In this position , its white to move. White’s knight has a nice square on e5 but Black is ready to kick it with …f6 and …e5. Black’s bishop will get some fresh air and White would lose the advantage.Steinitz found the right idea because more natural options would give Black a reasonable position.
So his creating an outpost maneuver can be considered as prophylaxis. And it was possible only because of the weakness of the d6-square.