"letterbox format" meaning in English

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  "lang_code": "en",
  "pos": "noun",
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        {
          "kind": "topical",
          "langcode": "en",
          "name": "Film",
          "orig": "en:Film",
          "parents": [
            "Entertainment",
            "Mass media",
            "Culture",
            "Media",
            "Society",
            "Communication",
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            "Fundamental"
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      "glosses": [
        "Synonym of letterboxing"
      ],
      "id": "en-letterbox_format-en-noun-~rIco6S-",
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          "film",
          "film#Noun"
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          "letterboxing",
          "letterboxing#English"
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      "raw_glosses": [
        "(film) Synonym of letterboxing"
      ],
      "synonyms": [
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          "tags": [
            "synonym",
            "synonym-of"
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          "word": "letterboxing"
        }
      ],
      "topics": [
        "broadcasting",
        "film",
        "media",
        "television"
      ]
    }
  ],
  "word": "letterbox format"
}

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      "expansion": "letterbox format",
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  "lang_code": "en",
  "pos": "noun",
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      "glosses": [
        "Synonym of letterboxing"
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          "letterboxing",
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        "(film) Synonym of letterboxing"
      ],
      "synonyms": [
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          "word": "letterboxing"
        }
      ],
      "topics": [
        "broadcasting",
        "film",
        "media",
        "television"
      ]
    }
  ],
  "word": "letterbox format"
}