"ㄨ" meaning in Translingual

{
  "head_templates": [
    {
      "args": {
        "sc": "Bopo"
      },
      "expansion": "ㄨ",
      "name": "mul-letter"
    }
  ],
  "lang": "Translingual",
  "lang_code": "mul",
  "pos": "character",
  "senses": [
    {
      "glosses": [
        "type: medial"
      ],
      "id": "en-ㄨ-mul-character-EiDOtZM2",
      "tags": [
        "letter"
      ]
    },
    {
      "categories": [
        {
          "_dis": "13 64 23",
          "kind": "other",
          "name": "Translingual entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        },
        {
          "_dis": "21 64 15",
          "kind": "other",
          "name": "Translingual terms with redundant script codes",
          "parents": [
            "Terms with redundant script codes",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        }
      ],
      "glosses": [
        "general transliteration: u"
      ],
      "id": "en-ㄨ-mul-character-7ZYEL0MW",
      "tags": [
        "letter"
      ]
    },
    {
      "glosses": [
        "keyboard key: J"
      ],
      "id": "en-ㄨ-mul-character-4Mkpulkh",
      "tags": [
        "letter"
      ]
    }
  ],
  "word": "ㄨ"
}

{
  "categories": [
    "Translingual entries with incorrect language header",
    "Translingual lemmas",
    "Translingual letters",
    "Translingual terms with redundant script codes",
    "Zhuyin script characters"
  ],
  "head_templates": [
    {
      "args": {
        "sc": "Bopo"
      },
      "expansion": "ㄨ",
      "name": "mul-letter"
    }
  ],
  "lang": "Translingual",
  "lang_code": "mul",
  "pos": "character",
  "senses": [
    {
      "glosses": [
        "type: medial"
      ],
      "tags": [
        "letter"
      ]
    },
    {
      "glosses": [
        "general transliteration: u"
      ],
      "tags": [
        "letter"
      ]
    },
    {
      "glosses": [
        "keyboard key: J"
      ],
      "tags": [
        "letter"
      ]
    }
  ],
  "word": "ㄨ"
}