"RM" meaning in Spanish

{
  "head_templates": [
    {
      "args": {
        "1": "f",
        "2": "-"
      },
      "expansion": "RM f (uncountable)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "resonancia magnética"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "Spanish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Initialism of resonancia magnética."
      ],
      "id": "en-RM-es-noun-AHwL0hDd",
      "links": [
        [
          "resonancia magnética",
          "resonancia magnética#Spanish"
        ]
      ],
      "tags": [
        "abbreviation",
        "alt-of",
        "feminine",
        "initialism",
        "uncountable"
      ],
      "wikipedia": [
        "RM"
      ]
    }
  ],
  "word": "RM"
}

{
  "head_templates": [
    {
      "args": {
        "1": "f",
        "2": "-"
      },
      "expansion": "RM f (uncountable)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "resonancia magnética"
        }
      ],
      "categories": [
        "Spanish entries with incorrect language header",
        "Spanish feminine nouns",
        "Spanish initialisms",
        "Spanish lemmas",
        "Spanish nouns",
        "Spanish uncountable nouns"
      ],
      "glosses": [
        "Initialism of resonancia magnética."
      ],
      "links": [
        [
          "resonancia magnética",
          "resonancia magnética#Spanish"
        ]
      ],
      "tags": [
        "abbreviation",
        "alt-of",
        "feminine",
        "initialism",
        "uncountable"
      ],
      "wikipedia": [
        "RM"
      ]
    }
  ],
  "word": "RM"
}