"equivalent class" meaning in English

{
  "forms": [
    {
      "form": "equivalent class"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Μαθηματικά (αγγλικά)",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "κλάση ισοδυναμίας"
      ],
      "id": "el-equivalent_class-en-noun-Ukxwx3wT",
      "raw_tags": [
        "μαθηματικά"
      ]
    }
  ],
  "word": "equivalent class"
}

{
  "forms": [
    {
      "form": "equivalent class"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Μαθηματικά (αγγλικά)"
      ],
      "glosses": [
        "κλάση ισοδυναμίας"
      ],
      "raw_tags": [
        "μαθηματικά"
      ]
    }
  ],
  "word": "equivalent class"
}