"1st grade" meaning in English

{
  "forms": [
    {
      "form": "1st grades",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "-",
        "2": "s"
      },
      "expansion": "1st grade (usually uncountable, plural 1st grades)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "first grade"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Alternative spelling of first grade"
      ],
      "id": "en-1st_grade-en-noun-4GSbqWcz",
      "links": [
        [
          "first grade",
          "first grade#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "uncountable",
        "usually"
      ]
    }
  ],
  "word": "1st grade"
}

{
  "forms": [
    {
      "form": "1st grades",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "-",
        "2": "s"
      },
      "expansion": "1st grade (usually uncountable, plural 1st grades)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "first grade"
        }
      ],
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms spelled with numbers",
        "English uncountable nouns"
      ],
      "glosses": [
        "Alternative spelling of first grade"
      ],
      "links": [
        [
          "first grade",
          "first grade#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "uncountable",
        "usually"
      ]
    }
  ],
  "word": "1st grade"
}