"dirty coal" meaning in English

{
  "etymology_text": "Due to the smell it gives off when burned.",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "dirty coal (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": "other",
          "name": "English entries with topic categories using raw markup",
          "parents": [
            "Entries with topic categories using raw markup",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms with non-redundant non-automated sortkeys",
          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Coal",
          "orig": "en:Coal",
          "parents": [
            "Fossil fuels",
            "Carbon",
            "Energy",
            "Natural resources",
            "Carbon group elements",
            "Nature",
            "Matter",
            "Chemical elements",
            "All topics",
            "Chemistry",
            "Fundamental",
            "Sciences"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1978 February 14, “Texas Turning to Its Reserves of Lignite”, in New York Times",
          "text": "Lignite's nickname “dirty coal,” suggests its one major drawback, but its allure is clearly its cost. Lignite is cheaper than most other energy sources.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "lignite"
      ],
      "id": "en-dirty_coal-en-noun-E-bBTk8V",
      "links": [
        [
          "lignite",
          "lignite"
        ]
      ],
      "raw_glosses": [
        "(informal) lignite"
      ],
      "tags": [
        "informal",
        "uncountable"
      ]
    }
  ],
  "word": "dirty coal"
}

{
  "etymology_text": "Due to the smell it gives off when burned.",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "dirty coal (uncountable)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English entries with topic categories using raw markup",
        "English informal terms",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with non-redundant non-automated sortkeys",
        "English terms with quotations",
        "English uncountable nouns",
        "en:Coal"
      ],
      "examples": [
        {
          "ref": "1978 February 14, “Texas Turning to Its Reserves of Lignite”, in New York Times",
          "text": "Lignite's nickname “dirty coal,” suggests its one major drawback, but its allure is clearly its cost. Lignite is cheaper than most other energy sources.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "lignite"
      ],
      "links": [
        [
          "lignite",
          "lignite"
        ]
      ],
      "raw_glosses": [
        "(informal) lignite"
      ],
      "tags": [
        "informal",
        "uncountable"
      ]
    }
  ],
  "word": "dirty coal"
}