"out of book" meaning in English

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  "lang_code": "en",
  "pos": "prep_phrase",
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          "word": "in book"
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          "name": "Chess",
          "orig": "en:Chess",
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        "No longer following commonly played theoretical lines analyzed in opening books; in territory unfamiliar to one or both of the players."
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        "(chess) No longer following commonly played theoretical lines analyzed in opening books; in territory unfamiliar to one or both of the players."
      ],
      "related": [
        {
          "word": "book move"
        }
      ],
      "synonyms": [
        {
          "word": "out of preparation"
        }
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        "board-games",
        "chess",
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  "word": "out of book"
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  "pos": "prep_phrase",
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      "word": "book move"
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          "word": "in book"
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        "(chess) No longer following commonly played theoretical lines analyzed in opening books; in territory unfamiliar to one or both of the players."
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        {
          "word": "out of preparation"
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  "word": "out of book"
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