Editing Glossary of chess (section)

==O==
{{glossary}}

{{term|term= occupation|content= occupation {{anchor|Occupation}} }}
{{defn|defn= Occupation of a rank or file means a rook or queen controls it; occupation of a square means a piece or pawn sits on it.<ref>Znosko-Borovsky 2012, pp. 118–19</ref><ref>Komarov & Djuric 2016, p.10</ref>}}

{{term|term= octopus|content= octopus {{anchor|Octopus}} }}
{{defn|defn= A strongly positioned knight in enemy territory. A knight not near the edge reaches out in eight directions, like the eight tentacles of an octopus.<ref>van de Oudeweetering 2014, p. 13</ref>}}

{{term|term= odds|content= [[Chess handicap|odds]] {{anchor|Odds}} }}
{{defn|defn= This refers to the stronger player giving the weaker player some sort of advantage in order to make the game more competitive. It may be an advantage in [[#material|material]], in extra moves, in time on the [[#chess clock|clock]], or some combination of those elements. Since the advent of the chess clock, time odds have become more common than material odds.<ref>Keene 1989, p. 182</ref>}}

{{term|term= offhand game|content= offhand game {{anchor|Offhand game|offhand games}} }}
{{defn|defn= See ''[[#skittles|skittles]]''.}}

{{term|term= Olympiad|content= [[Chess Olympiad|Olympiad]] {{anchor|Olympiad|Olympiads}} }}
{{defn|defn= An international team chess tournament organized biennially by [[#FIDE|FIDE]]. Each team represents a FIDE member country.}}

{{Chess diagram small
| tright
|
|rd|nd|bd|qd|kd|bd|nd|rd
|pd|pd|pd|  |  |pd|pd|pd
|  |  |  |  |  |  |  |
|  |  |  |pd|  |  |  |
|  |  |  |pl|  |  |  |
|  |  |  |  |  |  |  |
|pl|pl|pl|  |  |pl|pl|pl
|rl|nl|bl|ql|kl|bl|nl|rl
| The e-file is open in the [[French Defence#Exchange Variation|French Defense, Exchange Variation]] after 3.exd5 exd5.
}}
{{term|term= open file|content= [[open file]] {{anchor|Open file|open files|Open files}} }}
{{defn|defn= A [[#file|file]] on which there are no [[#pawn|pawns]].<ref name="Staunton 2014, p. 59">Staunton 2014, p. 59</ref> Cf. ''[[#half-open file|half-open file]]''.}}

{{term|term= open game|content= open game {{anchor|open game|open games|open position|open positions}} }}
{{defn|defn= A game in which exchanges have opened files and diagonals, and there are few pawns in the center, as opposed to a ''[[#closed game|closed game]]''.<ref name="Silman 1999, p. 437">Silman 1999, p. 437</ref> See also ''[[#positional play|positional play]]''.}}

{{term|term= Open Game|content= [[Open Game]] {{anchor|Open Game|Open Games}} }}
{{defn|defn= Any [[#opening|opening]] that begins with the moves 1.e4 e5. Examples of Open Games include the [[Ruy Lopez]], the [[Giuoco Piano]], the [[Danish Gambit]], and many others. The Open Game is also referred to as a ''Double King's Pawn Opening'' or ''Double King's Pawn Game''.}}

{{term|term= opening|content= [[Chess opening|opening]] {{anchor|Opening|openings}} }}
{{defn|defn= The beginning phase of the game, roughly the first dozen moves, but it can extend much farther. In the opening players set up their [[#pawn structure|pawn structures]], [[#development|develop]] their pieces, and usually [[castling|castle]]. The opening precedes the [[#middlegame|middlegame]].<ref name="Silman 1999, p. 437">Silman 1999, p. 437</ref>}}

{{term|term= opening innovation|content= opening innovation {{anchor|Opening innovation|opening innovations}} }}
{{defn|defn= A synonym for ''[[#theoretical novelty|theoretical novelty]]''.}}

{{term|term= opening preparation|content= opening preparation {{anchor|Opening preparation|opening preparations}} }}
{{defn|defn= Home study and analysis of [[#opening|openings]] and defenses that one expects to play, or meet, in later tournament or match games. In high-level play, an important part of this is the search for [[#theoretical novelty|theoretical novelties]] that improve upon previous play or previously published analysis.<ref>Schiller 2003, p. 19</ref>}}

{{term|term= opening repertoire|content= opening repertoire {{anchor|Opening repertoire|opening repertoires}} }}
{{defn|defn= The set of [[#opening|openings]] played by a particular player. The breadth of different players' repertoires varies from very narrow to very broad.<ref>Pandolfini 1996, p. 166</ref>}}

{{term|term= opening system|content= opening system {{anchor|Opening system|opening systems}} }}
{{defn|defn= An [[#opening|opening]] that is defined by one player's moves and that can be played generally regardless of the moves of the opponent, with the goal of reaching a desired type of [[#middlegame|middlegame]] position. Sometimes several different [[#move order|move orders]] are possible. Examples include the [[Colle System]] and [[Hippopotamus Defense]].<ref>Hooper & Whyld 1996, p. 405</ref>}}

{{term|term= open lines|content= open lines {{anchor|Open lines|open line}} }}
{{defn|no=1|defn= ''n''. Unobstructed [[#file|files]] and [[#diagonal|diagonals]]. See also ''[[#open game|open game]]''.}} 
{{defn|no=2|defn= ''v''. To move or exchange pawns to bring about unobstructed files and diagonals.}}

{{term|term= open tournament|content= open tournament {{anchor|Open tournament|open tournaments}} }}
{{defn|defn= A tournament where anyone can enter, regardless of rating or invitation.<ref>Pandolfini 1996, p. 167</ref> Cf. ''[[#closed tournament|closed tournament]]''.}}

{{term|term= opposite castling|content= [[Castling#Strategy|opposite castling]] {{anchor|Opposite castling|opposite-side castling|Opposite-side castling}} }}
{{defn|defn= Or '''opposite-side castling'''. Describes when one player has castled [[#kingside|kingside]] and the opponent has castled [[#queenside|queenside]].}}

{{term|term= opposite-colored bishops|content= opposite-colored bishops {{anchor|Opposite-colored bishops|opposite-coloured bishops|Opposite-coloured bishops|Opposite color bishops|Opposite colour bishops|Opposite colored bishops|Opposite coloured bishops}} }}
{{defn|defn= See ''[[#bishops on opposite colors|bishops on opposite colors]]''.}}

{{term|term= opposition|content= [[Opposition (chess)|opposition]] {{anchor|Opposition}} }}
{{defn|defn= A position in which two kings stand on the same rank, file, or diagonal with one empty square between them. The player to move may be forced to move the king to a less advantageous square. Opposition is a particularly important concept in [[#endgame|endgames]].<ref>Staunton 2014, p. 60</ref> One orthogonal square separation is ''direct opposition''; one diagonal square is ''diagonal opposition''; multiple squares separation is ''distant opposition''. Cf. ''[[#corresponding squares|corresponding squares]]''.}}

{{term|term= optimal play|content= optimal play {{anchor|Optimal play}} }}
{{defn|defn= See [[Best response]]. Both sides playing their best move at each turn, or one of equally good alternatives. One side tries to win as quickly as possible while the other side tries to delay it as long as possible, or optimal play may result in a draw. Cf. {{seclink|Solved game|Perfect play}}.}}

{{term|term= OTB|content = OTB {{anchor|OTB}} }}
{{defn|defn= An abbreviation for [[#over the board|over the board]].<ref name="Webb 2006, p. 72">Webb 2006, p. 72</ref>}}

{{term|term= outpost|content= [[Outpost (chess)|outpost]] {{anchor|Outpost|outposts}} }}
{{defn|defn= An outpost is a square protected by a pawn that is in or near the enemy's stronghold. Outposts are a favorable position from which one can launch an attack, particularly using a knight.<ref>Pandolfini 1992, p. 113</ref>}}

{{term|term= outside passed pawn|content= [[Passed pawn#Outside passed pawn|outside passed pawn]] {{anchor|Outside passed pawn|outside passed pawns}} }}
{{defn|defn= A [[#passed pawn|passed pawn]] near the edge of the board and not in the path of threats from the opponent's pawns. In the [[#endgame|endgame]], such a pawn can constitute a strong advantage, because it threatens to promote, and it also diverts the opponent's forces to restrain its advance.<ref>Pandolfini 2009, p. 305</ref>}}

{{term|term= overextended|content= overextended {{anchor|Overextended}} }}
{{defn|defn= An overextended position results when a player has advanced pawns too far into the opponent's side without sufficient support. The premature advance can leave weaknesses in the player's camp or the advanced pawns themselves may be weak ("overextended pawns").<ref>Seirwan & Silman 2005, p. 246; Horton 1959, p. 147</ref>}}

{{term|term= overloaded|content= [[Overloading (chess)|overloaded]] {{anchor|Overloaded|overloading|Overloading}} }}
{{defn|defn= A piece that has too many defensive duties. An overloaded piece can sometimes be [[#deflect|deflected]], or required to abandon one of its defensive duties.<ref>Pandolfini 1992, p. 237</ref>}}

{{term|term= overprotection|content= overprotection {{anchor|Overprotection}} }}
{{defn|defn= The strategy of protecting an important pawn or square more than is apparently necessary. This serves to dissuade the opponent from attacking that point, and the latent power of the "over protectors" assembled around an important point is a significant threat that can bear fruit at a small tactical change in the position. [[Aron Nimzowitsch]] coined the term and was a proponent of overprotection.<ref name="Silman 1999, p. 438">Silman 1999, p. 438</ref>}}

{{term|term= over the board|content= over the board {{anchor|Over the board|over the board (OTB)|over-the-board|Over-the-board}} }}
{{defn|no=1|defn= An over-the-board game is played face to face with the opponent, as opposed to a remote opponent as in [[Internet chess server|online chess]] or [[#correspondence chess|correspondence chess]].}}
{{defn|no=2|defn= Analysis carried out during a game in real time (not necessarily a face-to-face game) as opposed to during [[#prepared variation|preparation]]. Finding accurate moves over the board is harder than finding them with computer assistance in one's own time. "I looked up the [[#gambit|gambit]] Smith played and there's a [[#line|line]] that [[#refute|refutes]] it, but I couldn't find it over the board."<ref name="Webb 2006, p. 72">Webb 2006, p. 72</ref>}}
{{defn|Abbr. OTB.}}

{{term|term= overworked|content= overworked {{anchor|Overworked}} }}
{{defn|defn= See ''[[#overloaded|overloaded]]''.<ref>Seirawan & Silman 1994, p. 246; Brace 1977, p. 208; Horton 1959, p. 147</ref>}}
{{glossary end}}