"functional reserve" meaning in English

{
  "forms": [
    {
      "form": "functional reserves",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "functional reserve (plural functional reserves)",
      "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": "topical",
          "langcode": "en",
          "name": "Medicine",
          "orig": "en:Medicine",
          "parents": [
            "Biology",
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "The remaining capacity of an organ or body part to fulfil its physiological activity; (especially) in the context of disease, ageing, or impairment."
      ],
      "id": "en-functional_reserve-en-noun-vtNfPygk",
      "links": [
        [
          "medicine",
          "medicine"
        ],
        [
          "capacity",
          "capacity"
        ],
        [
          "fulfil",
          "fulfil"
        ],
        [
          "context",
          "context"
        ],
        [
          "ageing",
          "ageing"
        ],
        [
          "impairment",
          "impairment"
        ]
      ],
      "raw_glosses": [
        "(medicine) The remaining capacity of an organ or body part to fulfil its physiological activity; (especially) in the context of disease, ageing, or impairment."
      ],
      "topics": [
        "medicine",
        "sciences"
      ]
    }
  ],
  "word": "functional reserve"
}

{
  "forms": [
    {
      "form": "functional reserves",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "functional reserve (plural functional reserves)",
      "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:Medicine"
      ],
      "glosses": [
        "The remaining capacity of an organ or body part to fulfil its physiological activity; (especially) in the context of disease, ageing, or impairment."
      ],
      "links": [
        [
          "medicine",
          "medicine"
        ],
        [
          "capacity",
          "capacity"
        ],
        [
          "fulfil",
          "fulfil"
        ],
        [
          "context",
          "context"
        ],
        [
          "ageing",
          "ageing"
        ],
        [
          "impairment",
          "impairment"
        ]
      ],
      "raw_glosses": [
        "(medicine) The remaining capacity of an organ or body part to fulfil its physiological activity; (especially) in the context of disease, ageing, or impairment."
      ],
      "topics": [
        "medicine",
        "sciences"
      ]
    }
  ],
  "word": "functional reserve"
}