"verdad de perogrullo" meaning in Spanish

{
  "etymology_text": "From a medieval folkloric character named Pedro Grullo, also written as Pedrogrullo, Pero Grullo or Perogrullo. The exact origin of the character is unknown.",
  "forms": [
    {
      "form": "verdades de perogrullo",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "f"
      },
      "expansion": "verdad de perogrullo f (plural verdades de perogrullo)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Spanish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "truism"
      ],
      "id": "en-verdad_de_perogrullo-es-noun-ten3cDXg",
      "links": [
        [
          "truism",
          "truism"
        ]
      ],
      "related": [
        {
          "word": "perogrullada"
        },
        {
          "word": "perogrullear"
        }
      ],
      "synonyms": [
        {
          "word": "verdad de Perogrullo"
        },
        {
          "word": "verdad de Pero Grullo"
        }
      ],
      "tags": [
        "feminine"
      ]
    }
  ],
  "word": "verdad de perogrullo"
}

{
  "etymology_text": "From a medieval folkloric character named Pedro Grullo, also written as Pedrogrullo, Pero Grullo or Perogrullo. The exact origin of the character is unknown.",
  "forms": [
    {
      "form": "verdades de perogrullo",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "f"
      },
      "expansion": "verdad de perogrullo f (plural verdades de perogrullo)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "related": [
    {
      "word": "perogrullada"
    },
    {
      "word": "perogrullear"
    }
  ],
  "senses": [
    {
      "categories": [
        "Spanish countable nouns",
        "Spanish entries with incorrect language header",
        "Spanish feminine nouns",
        "Spanish lemmas",
        "Spanish multiword terms",
        "Spanish nouns"
      ],
      "glosses": [
        "truism"
      ],
      "links": [
        [
          "truism",
          "truism"
        ]
      ],
      "tags": [
        "feminine"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "verdad de Perogrullo"
    },
    {
      "word": "verdad de Pero Grullo"
    }
  ],
  "word": "verdad de perogrullo"
}