"book pocket" meaning in English

{
  "forms": [
    {
      "form": "book pockets",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "book pocket (plural book pockets)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "A pocket pasted inside the back cover of a book that holds a book card."
      ],
      "id": "en-book_pocket-en-noun-3W1jWUQ8",
      "links": [
        [
          "pocket",
          "pocket"
        ],
        [
          "pasted",
          "pasted"
        ],
        [
          "back cover",
          "back cover"
        ],
        [
          "book",
          "book"
        ],
        [
          "hold",
          "hold"
        ],
        [
          "card",
          "card"
        ]
      ],
      "qualifier": "library studies",
      "raw_glosses": [
        "(library studies) A pocket pasted inside the back cover of a book that holds a book card."
      ],
      "related": [
        {
          "word": "borrowing card"
        },
        {
          "word": "library card"
        }
      ]
    }
  ],
  "word": "book pocket"
}

{
  "forms": [
    {
      "form": "book pockets",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "book pocket (plural book pockets)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "borrowing card"
    },
    {
      "word": "library card"
    }
  ],
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "glosses": [
        "A pocket pasted inside the back cover of a book that holds a book card."
      ],
      "links": [
        [
          "pocket",
          "pocket"
        ],
        [
          "pasted",
          "pasted"
        ],
        [
          "back cover",
          "back cover"
        ],
        [
          "book",
          "book"
        ],
        [
          "hold",
          "hold"
        ],
        [
          "card",
          "card"
        ]
      ],
      "qualifier": "library studies",
      "raw_glosses": [
        "(library studies) A pocket pasted inside the back cover of a book that holds a book card."
      ]
    }
  ],
  "word": "book pocket"
}