"quadruple witching" meaning in English

{
  "etymology_text": "The idea of witching for these days is from the unusual patterns of trading that can occur ahead of the contract expiries.",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "quadruple witching (uncountable)",
      "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"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Finance",
          "orig": "en:Finance",
          "parents": [
            "Business",
            "Economics",
            "Society",
            "Social sciences",
            "All topics",
            "Sciences",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Simultaneous expiry on US markets of stock index futures, stock index options, stock options, and single stock futures, which takes place on the third Friday of March, June, September, and December. (Prior to single stock futures those days were triple witching.)"
      ],
      "id": "en-quadruple_witching-en-noun-ZvfqEJt5",
      "links": [
        [
          "finance",
          "finance#Noun"
        ],
        [
          "triple witching",
          "triple witching"
        ]
      ],
      "raw_glosses": [
        "(finance) Simultaneous expiry on US markets of stock index futures, stock index options, stock options, and single stock futures, which takes place on the third Friday of March, June, September, and December. (Prior to single stock futures those days were triple witching.)"
      ],
      "tags": [
        "uncountable"
      ],
      "topics": [
        "business",
        "finance"
      ]
    }
  ],
  "word": "quadruple witching"
}

{
  "etymology_text": "The idea of witching for these days is from the unusual patterns of trading that can occur ahead of the contract expiries.",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "quadruple witching (uncountable)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English uncountable nouns",
        "en:Finance"
      ],
      "glosses": [
        "Simultaneous expiry on US markets of stock index futures, stock index options, stock options, and single stock futures, which takes place on the third Friday of March, June, September, and December. (Prior to single stock futures those days were triple witching.)"
      ],
      "links": [
        [
          "finance",
          "finance#Noun"
        ],
        [
          "triple witching",
          "triple witching"
        ]
      ],
      "raw_glosses": [
        "(finance) Simultaneous expiry on US markets of stock index futures, stock index options, stock options, and single stock futures, which takes place on the third Friday of March, June, September, and December. (Prior to single stock futures those days were triple witching.)"
      ],
      "tags": [
        "uncountable"
      ],
      "topics": [
        "business",
        "finance"
      ]
    }
  ],
  "word": "quadruple witching"
}