"parallel key" meaning in English

{
  "forms": [
    {
      "form": "parallel keys",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "parallel key (plural parallel keys)",
      "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": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Music",
          "orig": "en:Music",
          "parents": [
            "Art",
            "Sound",
            "Culture",
            "Energy",
            "Society",
            "Nature",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A key with the same tonic as another key."
      ],
      "id": "en-parallel_key-en-noun-jH~R6X9Z",
      "links": [
        [
          "music",
          "music"
        ],
        [
          "key",
          "key"
        ],
        [
          "tonic",
          "tonic"
        ]
      ],
      "raw_glosses": [
        "(music, chiefly in the plural) A key with the same tonic as another key."
      ],
      "tags": [
        "in-plural"
      ],
      "topics": [
        "entertainment",
        "lifestyle",
        "music"
      ]
    }
  ],
  "word": "parallel key"
}

{
  "forms": [
    {
      "form": "parallel keys",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "parallel key (plural parallel keys)",
      "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",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Music"
      ],
      "glosses": [
        "A key with the same tonic as another key."
      ],
      "links": [
        [
          "music",
          "music"
        ],
        [
          "key",
          "key"
        ],
        [
          "tonic",
          "tonic"
        ]
      ],
      "raw_glosses": [
        "(music, chiefly in the plural) A key with the same tonic as another key."
      ],
      "tags": [
        "in-plural"
      ],
      "topics": [
        "entertainment",
        "lifestyle",
        "music"
      ]
    }
  ],
  "word": "parallel key"
}