"relative complement" meaning in English

{
  "forms": [
    {
      "form": "relative complements",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "relative complement (plural relative complements)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Set theory",
          "orig": "en:Set theory",
          "parents": [
            "Mathematics",
            "Formal sciences",
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "The set containing exactly those elements belonging to B but not to A."
      ],
      "id": "en-relative_complement-en-noun-mb~XpcX2",
      "links": [
        [
          "set theory",
          "set theory"
        ],
        [
          "set",
          "set"
        ],
        [
          "element",
          "element"
        ]
      ],
      "raw_glosses": [
        "(set theory, of set A \"in\" set B) The set containing exactly those elements belonging to B but not to A."
      ],
      "raw_tags": [
        "of set A \"in\" set B"
      ],
      "related": [
        {
          "word": "relative pseudo-complement"
        }
      ],
      "synonyms": [
        {
          "word": "set-theoretic difference"
        }
      ],
      "topics": [
        "mathematics",
        "sciences",
        "set-theory"
      ],
      "translations": [
        {
          "code": "cs",
          "lang": "Czech",
          "sense": "set of elements contained in one set but not another",
          "tags": [
            "masculine"
          ],
          "word": "množinový rozdíl"
        },
        {
          "code": "da",
          "lang": "Danish",
          "sense": "set of elements contained in one set but not another",
          "tags": [
            "common-gender"
          ],
          "word": "mængdedifferens"
        },
        {
          "code": "fi",
          "lang": "Finnish",
          "sense": "set of elements contained in one set but not another",
          "word": "joukkoerotus"
        },
        {
          "code": "is",
          "lang": "Icelandic",
          "sense": "set of elements contained in one set but not another",
          "tags": [
            "masculine"
          ],
          "word": "mengjamunur"
        },
        {
          "code": "is",
          "lang": "Icelandic",
          "sense": "set of elements contained in one set but not another",
          "tags": [
            "masculine"
          ],
          "word": "mengjamismunur"
        },
        {
          "code": "it",
          "lang": "Italian",
          "sense": "set of elements contained in one set but not another",
          "tags": [
            "masculine"
          ],
          "word": "complemento relativo"
        },
        {
          "alt": "さしゅうごう",
          "code": "ja",
          "lang": "Japanese",
          "roman": "sashūgō",
          "sense": "set of elements contained in one set but not another",
          "word": "差集合"
        },
        {
          "code": "ro",
          "lang": "Romanian",
          "sense": "set of elements contained in one set but not another",
          "tags": [
            "neuter"
          ],
          "word": "complement relativ"
        }
      ]
    }
  ],
  "word": "relative complement"
}

{
  "forms": [
    {
      "form": "relative complements",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "relative complement (plural relative complements)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "relative pseudo-complement"
    }
  ],
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "en:Set theory"
      ],
      "glosses": [
        "The set containing exactly those elements belonging to B but not to A."
      ],
      "links": [
        [
          "set theory",
          "set theory"
        ],
        [
          "set",
          "set"
        ],
        [
          "element",
          "element"
        ]
      ],
      "raw_glosses": [
        "(set theory, of set A \"in\" set B) The set containing exactly those elements belonging to B but not to A."
      ],
      "raw_tags": [
        "of set A \"in\" set B"
      ],
      "topics": [
        "mathematics",
        "sciences",
        "set-theory"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "set-theoretic difference"
    }
  ],
  "translations": [
    {
      "code": "cs",
      "lang": "Czech",
      "sense": "set of elements contained in one set but not another",
      "tags": [
        "masculine"
      ],
      "word": "množinový rozdíl"
    },
    {
      "code": "da",
      "lang": "Danish",
      "sense": "set of elements contained in one set but not another",
      "tags": [
        "common-gender"
      ],
      "word": "mængdedifferens"
    },
    {
      "code": "fi",
      "lang": "Finnish",
      "sense": "set of elements contained in one set but not another",
      "word": "joukkoerotus"
    },
    {
      "code": "is",
      "lang": "Icelandic",
      "sense": "set of elements contained in one set but not another",
      "tags": [
        "masculine"
      ],
      "word": "mengjamunur"
    },
    {
      "code": "is",
      "lang": "Icelandic",
      "sense": "set of elements contained in one set but not another",
      "tags": [
        "masculine"
      ],
      "word": "mengjamismunur"
    },
    {
      "code": "it",
      "lang": "Italian",
      "sense": "set of elements contained in one set but not another",
      "tags": [
        "masculine"
      ],
      "word": "complemento relativo"
    },
    {
      "alt": "さしゅうごう",
      "code": "ja",
      "lang": "Japanese",
      "roman": "sashūgō",
      "sense": "set of elements contained in one set but not another",
      "word": "差集合"
    },
    {
      "code": "ro",
      "lang": "Romanian",
      "sense": "set of elements contained in one set but not another",
      "tags": [
        "neuter"
      ],
      "word": "complement relativ"
    }
  ],
  "word": "relative complement"
}