"candidate key" meaning in English

{
  "antonyms": [
    {
      "word": "descriptor"
    }
  ],
  "etymology_text": ": candidate key <→ δείτε τις λέξεις candidate και key",
  "forms": [
    {
      "form": "candidate key"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "compound key"
    },
    {
      "word": "composite key"
    },
    {
      "word": "foreign key"
    }
  ],
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Βάσεις δεδομένων (αγγλικά)",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "συντομογραφία : CK"
        }
      ],
      "glosses": [
        ", (relational model), (relational database) το υποψήφιο κλειδί"
      ],
      "id": "el-candidate_key-en-noun-fFFN3plh",
      "raw_tags": [
        "βάσεις δεδομένων"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "key"
    }
  ],
  "word": "candidate key"
}

{
  "antonyms": [
    {
      "word": "descriptor"
    }
  ],
  "etymology_text": ": candidate key <→ δείτε τις λέξεις candidate και key",
  "forms": [
    {
      "form": "candidate key"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "compound key"
    },
    {
      "word": "composite key"
    },
    {
      "word": "foreign key"
    }
  ],
  "senses": [
    {
      "categories": [
        "Βάσεις δεδομένων (αγγλικά)"
      ],
      "examples": [
        {
          "text": "συντομογραφία : CK"
        }
      ],
      "glosses": [
        ", (relational model), (relational database) το υποψήφιο κλειδί"
      ],
      "raw_tags": [
        "βάσεις δεδομένων"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "key"
    }
  ],
  "word": "candidate key"
}