"sleeper hit" meaning in English

{
  "forms": [
    {
      "form": "sleeper hits",
      "tags": [
        "plural"
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      "expansion": "sleeper hit (plural sleeper hits)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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      "examples": [
        {
          "ref": "2008, John Berra, Declarations of independence : american cinema and the partiality of independent production:",
          "text": "It could be argued that there is no such thing as a 'sleeper' hit. It is industry terminology for a film which becomes a big success, despite having seemingly little promotion, and which plays successfully for a long time period, without having a record-breaking opening, or a run at the top of the box office chart.",
          "type": "quote"
        },
        {
          "ref": "2005, George Gimarc, Punk Diary: The Ultimate Trainspotter's Guide To Underground Rock, 1970-1982:",
          "text": "The record would be a minor hit in the U.S. (#49) but would, in time, become one of the most familiar songs of the decade. A 'sleeper' hit. It would not touch the UK charts at all.",
          "type": "quote"
        }
      ],
      "glosses": [
        "A work of entertainment that becomes successful only some time after its launch."
      ],
      "id": "en-sleeper_hit-en-noun-E6IncMHE",
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          "work",
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        [
          "entertainment",
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        [
          "successful",
          "successful"
        ],
        [
          "launch",
          "launch"
        ]
      ],
      "wikipedia": [
        "sleeper hit"
      ]
    }
  ],
  "word": "sleeper hit"
}

{
  "forms": [
    {
      "form": "sleeper hits",
      "tags": [
        "plural"
      ]
    }
  ],
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      "expansion": "sleeper hit (plural sleeper hits)",
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  "lang_code": "en",
  "pos": "noun",
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      "examples": [
        {
          "ref": "2008, John Berra, Declarations of independence : american cinema and the partiality of independent production:",
          "text": "It could be argued that there is no such thing as a 'sleeper' hit. It is industry terminology for a film which becomes a big success, despite having seemingly little promotion, and which plays successfully for a long time period, without having a record-breaking opening, or a run at the top of the box office chart.",
          "type": "quote"
        },
        {
          "ref": "2005, George Gimarc, Punk Diary: The Ultimate Trainspotter's Guide To Underground Rock, 1970-1982:",
          "text": "The record would be a minor hit in the U.S. (#49) but would, in time, become one of the most familiar songs of the decade. A 'sleeper' hit. It would not touch the UK charts at all.",
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        }
      ],
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        "A work of entertainment that becomes successful only some time after its launch."
      ],
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        [
          "launch",
          "launch"
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      "wikipedia": [
        "sleeper hit"
      ]
    }
  ],
  "word": "sleeper hit"
}