ChessWorld Hitchhiker's Guide to Chess

Scope: This glossary does not intend to cover player names, opening names, or Composition terms. The Glossary aims to relate the terms to ChessWorld where possible when giving examples.
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There is a dedicated Chess Openings Glossary

Glossary Course Modules with Game Examples

Glossary Course Modules with Tactical Puzzle Examples

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U

Underpromotion.
When promoting a pawn and, rather than choosing the Queen, selecting from Rook, Bishop or Knight. It may seem strange that underpromotion is a choice or where it would be advantageous. But, it is certainly a mistake to always think that promoting a pawn to a Queen is the only option. In certain positions it is important to consider the other pawn under-promotion choices.

Here is an example where it would be an advantage to underpromote to a Knight:-








Analyse position

Here White could promote to a queen, but that would not be as advantages, as underpromoting to a knight, in order to fork black's king and queen:-







Analyse position

There are other situations where promoting to a queen might cause a stalemate, and therefore it might be better to underpromote to avoid such a stalemate. Take the following example:-








Analyse position

Here White if promoting to a Queen without thinking would actually stalemate the Black king, and the result of the game would be a draw :-







Analyse position

So instead of promoting to a Queen, if White instead promotes to a Rook, then Black still has a move available as shown below:-







Analyse position

Black now has to play the only move which is Ka6, and White could then play Ra8 checkmate:







Analyse position



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Undouble
The term "undoubling" can apply to pieces which are on the same file. For example:-

When rooks are next to each other on a file, they are said to be "doubled". To "undouble" the rooks, is therefore to move one of them away from that file. For example:-








Analyse position

The rooks are currently "doubled". If White plays the move Rc1-b1, then the rooks are "undoubled".

It is commonly strategically advantageous to try and "undouble" pawns. In the following example, White's pawns are doubled:-







Analyse position

White can "undouble" the c pawns by playing the move cxd5. This would temporarily give White doubled d pawns. But on black's recapture, White has completely removed all doubled pawns.

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Unorthodox opening
An opening which is not commonly seen in Grandmaster play. An example is the Grob opening which starts with 1.g4 as the diagram below shows:-








Analyse position



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Unpin
To free a pinned piece from a pin. For example:-








Analyse position

The Black knight on f6 is pinned to the Queen. Black could "unpin" the Knight on f6 by playing the move Be7. This would make it more feasible for Black to move the knight on f6, as only the Bishop on e7 would risk being captured.

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Unsound
A term used to describe a strategy or tactic which is not quite correct because, if the opponent plays the best moves, it could be refuted. Sometimes it is advantageous to play unsoundly though when, for example, the opponent is in time pressure, and the unsound move alternative leads to greater complexity, or is difficult to refute.

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