Editing Chess opening (section)

{{Short description|Initial moves of a chess game}}
{{Refimprove|date=March 2021}}
{{Chess diagram
| tright
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|rd|nd|bd|qd|kd|bd|nd|rd
|pd|pd|pd|pd|pd|pd|pd|pd
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|pl|pl|pl|pl|pl|pl|pl|pl
|rl|nl|bl|ql|kl|bl|nl|rl
| The starting position of [[chess]]
}}

The '''opening''' is the initial stage of a [[chess]] game. It usually consists of established [[Chess_theory#Opening_theory|theory]]. The other phases are the [[chess middlegame|middlegame]] and the [[chess endgame|endgame]].<ref>{{Cite web|title=Phases of the game - Chess Strategy Online|url=https://www.chessstrategyonline.com/content/tutorials/basic-chess-concepts-phases-of-the-game|access-date=2021-03-30|website=www.chessstrategyonline.com}}</ref> Many opening sequences, known as ''openings'', have standard names such as "[[Sicilian Defense]]". ''[[The Oxford Companion to Chess]]'' lists 1,327 named openings and variants, and there are many others with varying degrees of common usage.<ref>{{cite book|last1=Hooper|first1=David|author1-link=David Vincent Hooper |last2=Whyld |first2=Kenneth |author2-link=Kenneth Whyld|year=1992 |title=The Oxford Companion to Chess|edition=2|publisher=Oxford University Press|isbn=0-19-280049-3|pages=[https://archive.org/details/oxfordcompaniont0000hoop/page/461 461]–480|title-link=The Oxford Companion to Chess}}</ref>

Opening moves that are considered standard are referred to as "book moves", or simply "book".<ref name=":0">{{Cite web|title=Book Move - Chess Terms|url=https://www.chess.com/terms/book-move-chess|access-date=2021-03-30|website=Chess.com|language=en-US}}</ref> When a game begins to deviate from known [[Chess theory#Opening theory|opening theory]], the players are said to be "out of book".<ref name=":0" /> In some openings, book lines have been worked out for over 30 moves, such as some lines in the classical [[King's Indian Defense]] and in the [[Sicilian Defense, Najdorf Variation|Najdorf Variation]] of the Sicilian Defense.<ref>[[Garry Kasparov]], ''[[My Great Predecessors#Modern Chess|Modern Chess]]'' part 1, p. 353</ref>
 
Professional chess players spend years studying openings, and they continue doing so throughout their careers as opening theory continues to evolve. Players at the club level also study openings, but the importance of the opening phase is less there since games are rarely decided in the opening. The study of openings can become unbalanced if it is to the exclusion of [[Chess tactic|tactical]] training and middlegame and endgame strategy.<ref name="won and lost">{{cite book |last=Hansen |first=Lars Bo|title=How Chess Games are Won and Lost|publisher=Gambit|date=October 7, 2008|isbn=978-1-906454-01-2}}</ref>

A new sequence of moves in the opening is referred to as a ''{{chessgloss|theoretical novelty}}''. When kept secret until used in a competitive game, it is often known as a ''prepared variation'', a powerful weapon in top-class competition.<ref name="Fine1952WorldsGreatChessGames">{{cite book|author=Fine, R.|title=The World's Great Chess Games|year=1952|publisher=Andre Deutsch (now as paperback from Dover)|isbn=0-679-13046-2}}</ref>
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