"上代特殊仮名遣い" meaning in Japanese

{
  "forms": [
    {
      "form": "上代特殊假名遣い",
      "tags": [
        "alternative",
        "kanji",
        "kyūjitai"
      ]
    }
  ],
  "lang": "Japanese",
  "lang_code": "ja",
  "pos": "soft-redirect",
  "redirects": [
    "上代特殊仮名遣"
  ],
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Japanese terms read with irregular kanji readings",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Japanese terms with non-redundant non-automated sortkeys",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Japanese terms with rendaku",
          "parents": [],
          "source": "w"
        }
      ],
      "id": "en-上代特殊仮名遣い-ja-soft-redirect-47DEQpj8",
      "tags": [
        "no-gloss"
      ]
    }
  ],
  "word": "上代特殊仮名遣い"
}

{
  "forms": [
    {
      "form": "上代特殊假名遣い",
      "tags": [
        "alternative",
        "kanji",
        "kyūjitai"
      ]
    }
  ],
  "lang": "Japanese",
  "lang_code": "ja",
  "pos": "soft-redirect",
  "redirects": [
    "上代特殊仮名遣"
  ],
  "senses": [
    {
      "categories": [
        "Japanese terms read with irregular kanji readings",
        "Japanese terms spelled with 上 read as じょう",
        "Japanese terms spelled with 代 read as だい",
        "Japanese terms spelled with 仮",
        "Japanese terms spelled with 名 read as な",
        "Japanese terms spelled with 殊 read as しゅ",
        "Japanese terms spelled with 特 read as とく",
        "Japanese terms spelled with 遣 read as つか",
        "Japanese terms with non-redundant non-automated sortkeys",
        "Japanese terms with rendaku"
      ],
      "tags": [
        "no-gloss"
      ]
    }
  ],
  "word": "上代特殊仮名遣い"
}