".arpa" meaning in Translingual

{
  "etymology_text": "Originally an acronym for Advanced Research Projects Agency; now said to stand for Address and Routing Parameter Area.",
  "head_templates": [
    {
      "args": {
        "1": "mul",
        "2": "noun"
      },
      "expansion": ".arpa",
      "name": "head"
    }
  ],
  "lang": "Translingual",
  "lang_code": "mul",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Translingual entries with incorrect language header",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "langcode": "mul",
          "name": "Internet",
          "orig": "mul:Internet",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "An Internet top-level domain used exclusively for technical infrastructure purposes."
      ],
      "id": "en-.arpa-mul-noun-JcCF1qxZ",
      "links": [
        [
          "Internet",
          "Internet"
        ],
        [
          "top-level domain",
          "top-level domain"
        ],
        [
          "technical",
          "technical"
        ],
        [
          "infrastructure",
          "infrastructure"
        ]
      ],
      "raw_glosses": [
        "(Internet) An Internet top-level domain used exclusively for technical infrastructure purposes."
      ],
      "tags": [
        "Internet"
      ],
      "wikipedia": [
        ".arpa",
        "Advanced Research Projects Agency"
      ]
    }
  ],
  "word": ".arpa"
}

{
  "etymology_text": "Originally an acronym for Advanced Research Projects Agency; now said to stand for Address and Routing Parameter Area.",
  "head_templates": [
    {
      "args": {
        "1": "mul",
        "2": "noun"
      },
      "expansion": ".arpa",
      "name": "head"
    }
  ],
  "lang": "Translingual",
  "lang_code": "mul",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Pages with 1 entry",
        "Pages with entries",
        "Translingual entries with incorrect language header",
        "Translingual lemmas",
        "Translingual nouns",
        "Translingual terms spelled with .",
        "mul:Internet"
      ],
      "glosses": [
        "An Internet top-level domain used exclusively for technical infrastructure purposes."
      ],
      "links": [
        [
          "Internet",
          "Internet"
        ],
        [
          "top-level domain",
          "top-level domain"
        ],
        [
          "technical",
          "technical"
        ],
        [
          "infrastructure",
          "infrastructure"
        ]
      ],
      "raw_glosses": [
        "(Internet) An Internet top-level domain used exclusively for technical infrastructure purposes."
      ],
      "tags": [
        "Internet"
      ],
      "wikipedia": [
        ".arpa",
        "Advanced Research Projects Agency"
      ]
    }
  ],
  "word": ".arpa"
}