"grey literature" meaning in English

{
  "forms": [
    {
      "form": "gray literature",
      "tags": [
        "alternative",
        "US"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "grey literature (uncountable)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Entries with translation boxes",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Terms with Finnish translations",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Terms with French translations",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Terms with Mandarin translations",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Terms with Polish translations",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "langcode": "en",
          "name": "Sciences",
          "orig": "en:Sciences",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Materials and research produced by organizations outside of the traditional commercial or academic publishing and distribution channels."
      ],
      "id": "en-grey_literature-en-noun-7rgZFtzQ",
      "links": [
        [
          "Materials",
          "material"
        ],
        [
          "research",
          "research"
        ],
        [
          "organization",
          "organization"
        ],
        [
          "distribution",
          "distribution"
        ]
      ],
      "related": [
        {
          "word": "paraliterature"
        },
        {
          "word": "white paper"
        }
      ],
      "tags": [
        "uncountable"
      ],
      "translations": [
        {
          "code": "cmn",
          "lang": "Chinese Mandarin",
          "lang_code": "cmn",
          "roman": "huīsè wénxiàn",
          "sense": "materials",
          "word": "灰色文獻 /灰色文献"
        },
        {
          "code": "fi",
          "lang": "Finnish",
          "lang_code": "fi",
          "sense": "materials",
          "word": "harmaa kirjallisuus"
        },
        {
          "code": "fr",
          "lang": "French",
          "lang_code": "fr",
          "sense": "materials",
          "tags": [
            "feminine"
          ],
          "word": "littérature grise"
        },
        {
          "code": "pl",
          "lang": "Polish",
          "lang_code": "pl",
          "sense": "materials",
          "tags": [
            "feminine"
          ],
          "word": "szara literatura"
        }
      ]
    }
  ],
  "word": "grey literature"
}

{
  "forms": [
    {
      "form": "gray literature",
      "tags": [
        "alternative",
        "US"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "grey literature (uncountable)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "paraliterature"
    },
    {
      "word": "white paper"
    }
  ],
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English uncountable nouns",
        "Entries with translation boxes",
        "Pages with 1 entry",
        "Pages with entries",
        "Terms with Finnish translations",
        "Terms with French translations",
        "Terms with Mandarin translations",
        "Terms with Polish translations",
        "en:Sciences"
      ],
      "glosses": [
        "Materials and research produced by organizations outside of the traditional commercial or academic publishing and distribution channels."
      ],
      "links": [
        [
          "Materials",
          "material"
        ],
        [
          "research",
          "research"
        ],
        [
          "organization",
          "organization"
        ],
        [
          "distribution",
          "distribution"
        ]
      ],
      "tags": [
        "uncountable"
      ]
    }
  ],
  "translations": [
    {
      "code": "cmn",
      "lang": "Chinese Mandarin",
      "lang_code": "cmn",
      "roman": "huīsè wénxiàn",
      "sense": "materials",
      "word": "灰色文獻 /灰色文献"
    },
    {
      "code": "fi",
      "lang": "Finnish",
      "lang_code": "fi",
      "sense": "materials",
      "word": "harmaa kirjallisuus"
    },
    {
      "code": "fr",
      "lang": "French",
      "lang_code": "fr",
      "sense": "materials",
      "tags": [
        "feminine"
      ],
      "word": "littérature grise"
    },
    {
      "code": "pl",
      "lang": "Polish",
      "lang_code": "pl",
      "sense": "materials",
      "tags": [
        "feminine"
      ],
      "word": "szara literatura"
    }
  ],
  "word": "grey literature"
}