"undefined" meaning in English

{
  "antonyms": [
    {
      "word": "defined"
    }
  ],
  "categories": [
    {
      "kind": "other",
      "name": "Λέξεις με πρόθημα un- (αγγλικά)",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_text": ": undefined < un- + defined",
  "forms": [
    {
      "form": "undefined"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "glosses": [
        "απροσδιόριστος"
      ],
      "id": "el-undefined-en-adj-JSRe9QZL"
    },
    {
      "glosses": [
        "αόριστος, μη ορισμένος"
      ],
      "id": "el-undefined-en-adj-ReQHqK4b"
    },
    {
      "glosses": [
        "ακαθόριστος"
      ],
      "id": "el-undefined-en-adj-sNxTWRoe"
    },
    {
      "categories": [
        {
          "kind": "other",
          "name": "Πληροφορική (αγγλικά)",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "※ A variable declared without a value will have the value undefined (JavaScript tutorial)",
          "translation": "«Μια μεταβλητή που δηλώνεται χωρίς τιμή θα έχει ακαθόριστη τιμή»"
        }
      ],
      "glosses": [
        "δεν έχει οριστεί, αόριστος, ακαθόριστος , δεν έχει νόημα"
      ],
      "id": "el-undefined-en-adj-FkrSf5iI",
      "raw_tags": [
        "πληροφορική"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "indefinite"
    },
    {
      "word": "undefinable"
    }
  ],
  "word": "undefined"
}

{
  "antonyms": [
    {
      "word": "defined"
    }
  ],
  "categories": [
    "Λέξεις με πρόθημα un- (αγγλικά)"
  ],
  "etymology_text": ": undefined < un- + defined",
  "forms": [
    {
      "form": "undefined"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "glosses": [
        "απροσδιόριστος"
      ]
    },
    {
      "glosses": [
        "αόριστος, μη ορισμένος"
      ]
    },
    {
      "glosses": [
        "ακαθόριστος"
      ]
    },
    {
      "categories": [
        "Πληροφορική (αγγλικά)"
      ],
      "examples": [
        {
          "text": "※ A variable declared without a value will have the value undefined (JavaScript tutorial)",
          "translation": "«Μια μεταβλητή που δηλώνεται χωρίς τιμή θα έχει ακαθόριστη τιμή»"
        }
      ],
      "glosses": [
        "δεν έχει οριστεί, αόριστος, ακαθόριστος , δεν έχει νόημα"
      ],
      "raw_tags": [
        "πληροφορική"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "indefinite"
    },
    {
      "word": "undefinable"
    }
  ],
  "word": "undefined"
}