"index digit" meaning in English

{
  "forms": [
    {
      "form": "index digits",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "index digit (plural index digits)",
      "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": "lifeform",
          "langcode": "en",
          "name": "Animal body parts",
          "orig": "en:Animal body parts",
          "parents": [
            "Body parts",
            "Animals",
            "Body",
            "Anatomy",
            "Lifeforms",
            "Human",
            "Biology",
            "Medicine",
            "All topics",
            "Life",
            "Sciences",
            "Fundamental",
            "Nature"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "In other animals that digit corresponding to the human index finger."
      ],
      "id": "en-index_digit-en-noun-feXzwSV7",
      "links": [
        [
          "zootomy",
          "zootomy"
        ],
        [
          "human",
          "human"
        ],
        [
          "index finger",
          "index finger"
        ]
      ],
      "raw_glosses": [
        "(zootomy) In other animals that digit corresponding to the human index finger."
      ],
      "topics": [
        "biology",
        "natural-sciences",
        "zoology",
        "zootomy"
      ]
    }
  ],
  "word": "index digit"
}

{
  "forms": [
    {
      "form": "index digits",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "index digit (plural index digits)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "en:Animal body parts"
      ],
      "glosses": [
        "In other animals that digit corresponding to the human index finger."
      ],
      "links": [
        [
          "zootomy",
          "zootomy"
        ],
        [
          "human",
          "human"
        ],
        [
          "index finger",
          "index finger"
        ]
      ],
      "raw_glosses": [
        "(zootomy) In other animals that digit corresponding to the human index finger."
      ],
      "topics": [
        "biology",
        "natural-sciences",
        "zoology",
        "zootomy"
      ]
    }
  ],
  "word": "index digit"
}