"hidden track" meaning in English

{
  "forms": [
    {
      "form": "hidden tracks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "hidden track (plural hidden tracks)",
      "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": "Music",
          "orig": "en:Music",
          "parents": [
            "Art",
            "Sound",
            "Culture",
            "Energy",
            "Society",
            "Nature",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "2023, Jeff Gomez, There Was No Alternative: Generation X, AIDS, and the Making of a Classic Nineties Record, McFarland",
          "text": "Nirvana was no stranger to hidden tracks. Nevermind featured the abrasive jam “Endless, Nameless,” which appeared ten minutes after the last song, the quiet and contemplative “Something in the Way.” In 1991 hidden tracks were relatively rare but, in the wake of Nevermind's success and influence, they began appearing everywhere.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A piece of audio that has been placed on a medium, typically a CD, in such a way as to avoid detection by the casual listener."
      ],
      "id": "en-hidden_track-en-noun-0Kk4jozw",
      "links": [
        [
          "CD",
          "CD"
        ]
      ],
      "synonyms": [
        {
          "word": "ghost track"
        }
      ]
    }
  ],
  "word": "hidden track"
}

{
  "forms": [
    {
      "form": "hidden tracks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "hidden track (plural hidden tracks)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English entries with topic categories using raw markup",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with non-redundant non-automated sortkeys",
        "English terms with quotations",
        "en:Music"
      ],
      "examples": [
        {
          "ref": "2023, Jeff Gomez, There Was No Alternative: Generation X, AIDS, and the Making of a Classic Nineties Record, McFarland",
          "text": "Nirvana was no stranger to hidden tracks. Nevermind featured the abrasive jam “Endless, Nameless,” which appeared ten minutes after the last song, the quiet and contemplative “Something in the Way.” In 1991 hidden tracks were relatively rare but, in the wake of Nevermind's success and influence, they began appearing everywhere.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A piece of audio that has been placed on a medium, typically a CD, in such a way as to avoid detection by the casual listener."
      ],
      "links": [
        [
          "CD",
          "CD"
        ]
      ],
      "synonyms": [
        {
          "word": "ghost track"
        }
      ]
    }
  ],
  "word": "hidden track"
}