"hija del medio" meaning in Spanish

{
  "forms": [
    {
      "form": "hijas del medio",
      "tags": [
        "plural"
      ]
    },
    {
      "form": "hijo del medio",
      "tags": [
        "masculine"
      ]
    },
    {
      "form": "hijos del medio",
      "tags": [
        "masculine",
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "f",
        "m": "+"
      },
      "expansion": "hija del medio f (plural hijas del medio, masculine hijo del medio, masculine plural hijos del medio)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Spanish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "es",
          "name": "Family members",
          "orig": "es:Family members",
          "parents": [
            "Family",
            "People",
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "middle child, middle daughter"
      ],
      "id": "en-hija_del_medio-es-noun-fFfUhXpX",
      "links": [
        [
          "middle child",
          "middle child"
        ],
        [
          "middle",
          "middle"
        ],
        [
          "daughter",
          "daughter"
        ]
      ],
      "synonyms": [
        {
          "word": "hija mediana"
        }
      ],
      "tags": [
        "feminine"
      ]
    }
  ],
  "word": "hija del medio"
}

{
  "forms": [
    {
      "form": "hijas del medio",
      "tags": [
        "plural"
      ]
    },
    {
      "form": "hijo del medio",
      "tags": [
        "masculine"
      ]
    },
    {
      "form": "hijos del medio",
      "tags": [
        "masculine",
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "f",
        "m": "+"
      },
      "expansion": "hija del medio f (plural hijas del medio, masculine hijo del medio, masculine plural hijos del medio)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Spanish countable nouns",
        "Spanish entries with incorrect language header",
        "Spanish feminine nouns",
        "Spanish lemmas",
        "Spanish multiword terms",
        "Spanish nouns",
        "es:Family members"
      ],
      "glosses": [
        "middle child, middle daughter"
      ],
      "links": [
        [
          "middle child",
          "middle child"
        ],
        [
          "middle",
          "middle"
        ],
        [
          "daughter",
          "daughter"
        ]
      ],
      "synonyms": [
        {
          "word": "hija mediana"
        }
      ],
      "tags": [
        "feminine"
      ]
    }
  ],
  "word": "hija del medio"
}