An outpost is an advantage and happens when you have a piece, usually a knight that is camping out in the opponent's territory and is supported by a pawn and unable to get rid of or drive away without loss of material. Outposts can cause a great deal of trouble to your opponent by tying down pieces and making them passive and limiting their mobility. Sometimes if you are stuck with a annoying knight outpost, it is a good idea to just trade off the knight and pawn for a rook. Believe me, it will be worth it. Here is a example from one of my games.
In the end I won easily. Outposts are very strong!
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