"backing track" meaning in English

{
  "forms": [
    {
      "form": "backing tracks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "backing track (plural backing tracks)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Entries with translation boxes",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Terms with Polish translations",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "langcode": "en",
          "name": "Music",
          "orig": "en:Music",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "A prerecorded piece of music used to accompany a musician who sings live."
      ],
      "id": "en-backing_track-en-noun-8jZiig1t",
      "links": [
        [
          "prerecord",
          "prerecord"
        ],
        [
          "live",
          "live"
        ]
      ],
      "translations": [
        {
          "code": "pl",
          "lang": "Polish",
          "lang_code": "pl",
          "sense": "Translations",
          "tags": [
            "masculine"
          ],
          "word": "podkład"
        }
      ]
    }
  ],
  "word": "backing track"
}

{
  "forms": [
    {
      "form": "backing tracks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "backing track (plural backing tracks)",
      "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",
        "Entries with translation boxes",
        "Pages with 1 entry",
        "Pages with entries",
        "Terms with Polish translations",
        "Translation table header lacks gloss",
        "en:Music"
      ],
      "glosses": [
        "A prerecorded piece of music used to accompany a musician who sings live."
      ],
      "links": [
        [
          "prerecord",
          "prerecord"
        ],
        [
          "live",
          "live"
        ]
      ]
    }
  ],
  "translations": [
    {
      "code": "pl",
      "lang": "Polish",
      "lang_code": "pl",
      "sense": "Translations",
      "tags": [
        "masculine"
      ],
      "word": "podkład"
    }
  ],
  "word": "backing track"
}