"em space" meaning in English

{
  "forms": [
    {
      "form": "em spaces",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "em space (plural em spaces)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "langcode": "en",
          "name": "Typography",
          "orig": "en:Typography",
          "parents": [],
          "source": "w"
        }
      ],
      "coordinate_terms": [
        {
          "word": "en space"
        },
        {
          "word": "no-break space"
        },
        {
          "word": "thick space"
        },
        {
          "word": "thin space"
        },
        {
          "word": "word space"
        },
        {
          "word": "zero-width space"
        }
      ],
      "glosses": [
        "A space which has a nominal width of 1 em."
      ],
      "id": "en-em_space-en-noun-n9bi6UyC",
      "links": [
        [
          "typography",
          "typography"
        ],
        [
          "space",
          "space"
        ],
        [
          "em",
          "em"
        ]
      ],
      "raw_glosses": [
        "(typography) A space which has a nominal width of 1 em."
      ],
      "related": [
        {
          "word": "em dash"
        },
        {
          "word": "em quad"
        }
      ],
      "synonyms": [
        {
          "word": "em quad"
        },
        {
          "word": "mutton quad"
        },
        {
          "word": "quad"
        }
      ],
      "topics": [
        "media",
        "publishing",
        "typography"
      ]
    }
  ],
  "word": "em space"
}

{
  "forms": [
    {
      "form": "em spaces",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "em space (plural em spaces)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "em dash"
    },
    {
      "word": "em quad"
    }
  ],
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Typography"
      ],
      "coordinate_terms": [
        {
          "word": "en space"
        },
        {
          "word": "no-break space"
        },
        {
          "word": "thick space"
        },
        {
          "word": "thin space"
        },
        {
          "word": "word space"
        },
        {
          "word": "zero-width space"
        }
      ],
      "glosses": [
        "A space which has a nominal width of 1 em."
      ],
      "links": [
        [
          "typography",
          "typography"
        ],
        [
          "space",
          "space"
        ],
        [
          "em",
          "em"
        ]
      ],
      "raw_glosses": [
        "(typography) A space which has a nominal width of 1 em."
      ],
      "synonyms": [
        {
          "word": "em quad"
        },
        {
          "word": "mutton quad"
        },
        {
          "word": "quad"
        }
      ],
      "topics": [
        "media",
        "publishing",
        "typography"
      ]
    }
  ],
  "word": "em space"
}