"PUO" meaning in English

{
  "forms": [
    {
      "form": "PUOs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "PUO (plural PUOs)",
      "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"
        }
      ],
      "examples": [
        {
          "ref": "1933, Vera Brittain, Testament of Youth, Penguin, published 2005, page 402:",
          "text": "The particular “bug” that had assailed me was difficult to locate, but was obviously a form of “P.U.O.” or trench fever not dissimilar from the Malta disease in 1916.",
          "type": "quote"
        }
      ],
      "glosses": [
        "Pyrexia of unknown origin."
      ],
      "id": "en-PUO-en-noun-lcCW6dqN",
      "links": [
        [
          "Pyrexia",
          "pyrexia"
        ],
        [
          "unknown",
          "unknown"
        ],
        [
          "origin",
          "origin"
        ]
      ]
    }
  ],
  "word": "PUO"
}

{
  "forms": [
    {
      "form": "PUOs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "PUO (plural PUOs)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English nouns",
        "English terms with quotations",
        "Pages with 1 entry",
        "Pages with entries",
        "Quotation templates to be cleaned"
      ],
      "examples": [
        {
          "ref": "1933, Vera Brittain, Testament of Youth, Penguin, published 2005, page 402:",
          "text": "The particular “bug” that had assailed me was difficult to locate, but was obviously a form of “P.U.O.” or trench fever not dissimilar from the Malta disease in 1916.",
          "type": "quote"
        }
      ],
      "glosses": [
        "Pyrexia of unknown origin."
      ],
      "links": [
        [
          "Pyrexia",
          "pyrexia"
        ],
        [
          "unknown",
          "unknown"
        ],
        [
          "origin",
          "origin"
        ]
      ]
    }
  ],
  "word": "PUO"
}