"killer cancel" meaning in English

{
  "forms": [
    {
      "form": "killer cancels",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "killer cancel (plural killer cancels)",
      "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": "Philately",
          "orig": "en:Philately",
          "parents": [
            "Hobbies",
            "Recreation",
            "Human activity",
            "Human behaviour",
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A cancellation mark that is so heavy that it defaces the postage stamp to which it is applied, devaluing it from a collector's point of view."
      ],
      "id": "en-killer_cancel-en-noun-ajL0lKGc",
      "links": [
        [
          "philately",
          "philately"
        ],
        [
          "cancellation",
          "cancellation"
        ],
        [
          "deface",
          "deface"
        ],
        [
          "postage stamp",
          "postage stamp"
        ],
        [
          "collector",
          "collector"
        ]
      ],
      "raw_glosses": [
        "(philately) A cancellation mark that is so heavy that it defaces the postage stamp to which it is applied, devaluing it from a collector's point of view."
      ],
      "topics": [
        "hobbies",
        "lifestyle",
        "philately"
      ]
    }
  ],
  "word": "killer cancel"
}

{
  "forms": [
    {
      "form": "killer cancels",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "killer cancel (plural killer cancels)",
      "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",
        "en:Philately"
      ],
      "glosses": [
        "A cancellation mark that is so heavy that it defaces the postage stamp to which it is applied, devaluing it from a collector's point of view."
      ],
      "links": [
        [
          "philately",
          "philately"
        ],
        [
          "cancellation",
          "cancellation"
        ],
        [
          "deface",
          "deface"
        ],
        [
          "postage stamp",
          "postage stamp"
        ],
        [
          "collector",
          "collector"
        ]
      ],
      "raw_glosses": [
        "(philately) A cancellation mark that is so heavy that it defaces the postage stamp to which it is applied, devaluing it from a collector's point of view."
      ],
      "topics": [
        "hobbies",
        "lifestyle",
        "philately"
      ]
    }
  ],
  "word": "killer cancel"
}