"H3" meaning in Translingual

{
  "head_templates": [
    {
      "args": {
        "1": "mul",
        "2": "noun"
      },
      "expansion": "H3",
      "name": "head"
    }
  ],
  "lang": "Translingual",
  "lang_code": "mul",
  "pos": "noun",
  "related": [
    {
      "_dis1": "0 0",
      "word": "H1"
    },
    {
      "_dis1": "0 0",
      "word": "H2"
    },
    {
      "_dis1": "0 0",
      "word": "H4"
    }
  ],
  "senses": [
    {
      "glosses": [
        "histamine receptor #3, the third histamine receptor discovered."
      ],
      "id": "en-H3-mul-noun-vLcVV2FS",
      "links": [
        [
          "histamine",
          "histamine#English"
        ],
        [
          "receptor",
          "receptor#English"
        ]
      ]
    },
    {
      "alt_of": [
        {
          "word": "H-3"
        }
      ],
      "categories": [
        {
          "_dis": "31 69",
          "kind": "other",
          "name": "Translingual entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        }
      ],
      "glosses": [
        "Alternative form of H-3"
      ],
      "id": "en-H3-mul-noun-8dax2N7s",
      "links": [
        [
          "H-3",
          "H-3#Translingual"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "H3"
}

{
  "categories": [
    "Translingual entries with incorrect language header",
    "Translingual lemmas",
    "Translingual nouns",
    "Translingual terms spelled with numbers"
  ],
  "head_templates": [
    {
      "args": {
        "1": "mul",
        "2": "noun"
      },
      "expansion": "H3",
      "name": "head"
    }
  ],
  "lang": "Translingual",
  "lang_code": "mul",
  "pos": "noun",
  "related": [
    {
      "word": "H1"
    },
    {
      "word": "H2"
    },
    {
      "word": "H4"
    }
  ],
  "senses": [
    {
      "glosses": [
        "histamine receptor #3, the third histamine receptor discovered."
      ],
      "links": [
        [
          "histamine",
          "histamine#English"
        ],
        [
          "receptor",
          "receptor#English"
        ]
      ]
    },
    {
      "alt_of": [
        {
          "word": "H-3"
        }
      ],
      "glosses": [
        "Alternative form of H-3"
      ],
      "links": [
        [
          "H-3",
          "H-3#Translingual"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "H3"
}

{
  "called_from": "page/1412",
  "msg": "gloss may contain unhandled list items: histamine receptor #3, the third histamine receptor discovered.",
  "path": [
    "H3"
  ],
  "section": "Translingual",
  "subsection": "noun",
  "title": "H3",
  "trace": ""
}