Short side
The short side is the side of a pawn's file that has fewer files between it and the edge of the board, the opposite of the long side where more room is available.
Every pawn splits the board into two sides, and these sides are rarely equal. The short side is the one with fewer files between the pawn's file and the edge. For a pawn on the c-file, the short side is the a- and b-files, while the long side is everything from the d-file to the h-file.
The idea matters most in rook endings with a single pawn, when the defending king has to leave the pawn's file. The standard advice is to send the king to the short side and keep the rook on the long side, where it has room to check the attacking king from a distance.
Getting this backwards is a well-known way to lose. With the king on the long side, the rook is left on the short side, too close to the pawn to give useful checks from the side, and the attacking king can approach it or hide from it.
When you know which side is short, you can plan where your king and rook go before the checks begin, instead of finding out later that the rook has no room. Count the files on each side of the pawn first, then decide.
It sits close to Checking distance. Checking distance is the space a defending rook keeps from the enemy king, usually a long way off, so it can give a series of checks from the side or behind without being attacked.
A neighboring idea is Pawn breakthrough. A pawn breakthrough is a sacrifice of one or more pawns that tears open the opposing pawn chain so that a remaining pawn can run through and promote.
If "Short side" has cost you half a point, a first lesson is a good place to find the pattern behind it: George Li goes through your games and builds a plan.
Related terms
The long side is the side of a pawn's file with more files between it and the edge of the board, giving a rook more room to check from far away.
Checking distance is the space a defending rook keeps from the enemy king, usually a long way off, so it can give a series of checks from the side or behind without being attacked.
A rook endgame is an ending in which each side has a rook and some pawns and no other pieces, and it is the most common type of endgame, so its main ideas are worth learning early.
A rook pawn is a pawn on the a-file or the h-file, the edge of the board, which has fewer capture options and gives the attacker less room to maneuver.
The Lucena position is the key winning setup in rook and pawn against rook: the pawn stands on the seventh rank, its king sits on the promotion square, the enemy king is cut off, and building a bridge with the rook wins.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
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