"all clear" meaning in English

{
  "categories": [],
  "etymology_templates": [],
  "etymology_text": "all + clear",
  "forms": [
    {
      "form": "clears",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "all clear (countable and uncountable, plural all clears)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "glosses": [
        "a signal that danger, such as an air raid, is over; usually a siren at a single pitch"
      ],
      "id": "all_clear-en-noun-ZKR7RJGK",
      "raw_glosses": [
        "a signal that danger, such as an air raid, is over; usually a siren at a single pitch"
      ],
      "tags": [
        "countable",
        "uncountable"
      ]
    },
    {
      "glosses": [
        "permission to proceed after obstacles have been removed"
      ],
      "id": "all_clear-en-noun-XTCmJVkx",
      "raw_glosses": [
        "permission to proceed after obstacles have been removed"
      ],
      "tags": [
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "all clear"
}

{
  "categories": [
    "English countable nouns",
    "English lemmas",
    "English multiword terms",
    "English nouns",
    "English uncountable nouns"
  ],
  "etymology_templates": [],
  "etymology_text": "all + clear",
  "forms": [
    {
      "form": "clears",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "all clear (countable and uncountable, plural all clears)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "glosses": [
        "a signal that danger, such as an air raid, is over; usually a siren at a single pitch"
      ],
      "raw_glosses": [
        "a signal that danger, such as an air raid, is over; usually a siren at a single pitch"
      ],
      "tags": [
        "countable",
        "uncountable"
      ]
    },
    {
      "glosses": [
        "permission to proceed after obstacles have been removed"
      ],
      "raw_glosses": [
        "permission to proceed after obstacles have been removed"
      ],
      "tags": [
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "all clear"
}