"core day" meaning in English

{
  "forms": [
    {
      "form": "core days",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "core day (plural core days)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "coordinate_terms": [
        {
          "word": "list in leg day"
        }
      ],
      "examples": [
        {
          "ref": "2021 August 17, Morit Summers, Big & Bold: Strength Training for the Plus-Size Woman, Human Kinetics, page 147",
          "text": "... leg day, back day, and core day.",
          "type": "quotation"
        },
        {
          "ref": "2022 November 24, Kenneth Kollasch, Beating Average: A Story to Extraordinary, WestBow Press",
          "text": "... leg day, cardio day, core day, chest day, and all the rest! But, have you ever taken a day to workout your tongue? We all know communication is vital to success in anything, and it is literally life or death when it comes to warfare[…]",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A day dedicated to exercising one's core."
      ],
      "id": "en-core_day-en-noun-5o3OJ2jI",
      "links": [
        [
          "exercising",
          "exercise"
        ]
      ]
    }
  ],
  "word": "core day"
}

{
  "coordinate_terms": [
    {
      "word": "list in leg day"
    }
  ],
  "forms": [
    {
      "form": "core days",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "core day (plural core days)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations"
      ],
      "examples": [
        {
          "ref": "2021 August 17, Morit Summers, Big & Bold: Strength Training for the Plus-Size Woman, Human Kinetics, page 147",
          "text": "... leg day, back day, and core day.",
          "type": "quotation"
        },
        {
          "ref": "2022 November 24, Kenneth Kollasch, Beating Average: A Story to Extraordinary, WestBow Press",
          "text": "... leg day, cardio day, core day, chest day, and all the rest! But, have you ever taken a day to workout your tongue? We all know communication is vital to success in anything, and it is literally life or death when it comes to warfare[…]",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A day dedicated to exercising one's core."
      ],
      "links": [
        [
          "exercising",
          "exercise"
        ]
      ]
    }
  ],
  "word": "core day"
}