"imaginaire pur" meaning in French

{
  "forms": [
    {
      "form": "imaginaires purs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "m"
      },
      "expansion": "imaginaire pur m (plural imaginaires purs)",
      "name": "fr-noun"
    }
  ],
  "lang": "French",
  "lang_code": "fr",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "French entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "fr",
          "name": "Mathematics",
          "orig": "fr:Mathematics",
          "parents": [
            "Formal sciences",
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "Le nombre complexe i est un imaginaire pur.",
          "type": "example"
        }
      ],
      "glosses": [
        "imaginary number (number of the form ai)"
      ],
      "id": "en-imaginaire_pur-fr-noun-H6MMoA3~",
      "links": [
        [
          "mathematics",
          "mathematics"
        ],
        [
          "imaginary number",
          "imaginary number"
        ]
      ],
      "raw_glosses": [
        "(mathematics) imaginary number (number of the form ai)"
      ],
      "tags": [
        "masculine"
      ],
      "topics": [
        "mathematics",
        "sciences"
      ]
    }
  ],
  "word": "imaginaire pur"
}

{
  "forms": [
    {
      "form": "imaginaires purs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "m"
      },
      "expansion": "imaginaire pur m (plural imaginaires purs)",
      "name": "fr-noun"
    }
  ],
  "lang": "French",
  "lang_code": "fr",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "French countable nouns",
        "French entries with incorrect language header",
        "French lemmas",
        "French masculine nouns",
        "French multiword terms",
        "French nouns",
        "French terms with usage examples",
        "Requests for translations of French usage examples",
        "fr:Mathematics"
      ],
      "examples": [
        {
          "text": "Le nombre complexe i est un imaginaire pur.",
          "type": "example"
        }
      ],
      "glosses": [
        "imaginary number (number of the form ai)"
      ],
      "links": [
        [
          "mathematics",
          "mathematics"
        ],
        [
          "imaginary number",
          "imaginary number"
        ]
      ],
      "raw_glosses": [
        "(mathematics) imaginary number (number of the form ai)"
      ],
      "tags": [
        "masculine"
      ],
      "topics": [
        "mathematics",
        "sciences"
      ]
    }
  ],
  "word": "imaginaire pur"
}