"σ-compact" meaning in English

{
  "etymology_text": "The 'σ' stands for \"countable union\".",
  "head_templates": [
    {
      "args": {
        "1": "-",
        "head": "σ-compact"
      },
      "expansion": "σ-compact (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms containing italics",
          "parents": [
            "Terms containing italics",
            "Terms by orthographic property",
            "Terms by lexical property"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms written in multiple scripts",
          "parents": [
            "Terms written in multiple scripts",
            "Terms by orthographic property",
            "Terms by lexical property"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Mathematical analysis",
          "orig": "en:Mathematical analysis",
          "parents": [
            "Mathematics",
            "Formal sciences",
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "That is expressible as a countable union of compact sets."
      ],
      "id": "en-σ-compact-en-adj-GwdVwTJW",
      "links": [
        [
          "mathematical analysis",
          "mathematical analysis"
        ],
        [
          "countable",
          "countable"
        ],
        [
          "union",
          "union"
        ],
        [
          "compact",
          "compact"
        ]
      ],
      "raw_glosses": [
        "(mathematical analysis, of a set in a topological space) That is expressible as a countable union of compact sets."
      ],
      "raw_tags": [
        "of a set in a topological space"
      ],
      "tags": [
        "not-comparable"
      ],
      "topics": [
        "mathematical-analysis",
        "mathematics",
        "sciences"
      ]
    }
  ],
  "word": "σ-compact"
}

{
  "etymology_text": "The 'σ' stands for \"countable union\".",
  "head_templates": [
    {
      "args": {
        "1": "-",
        "head": "σ-compact"
      },
      "expansion": "σ-compact (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        "English adjectives",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English terms containing italics",
        "English terms spelled with Σ",
        "English terms written in multiple scripts",
        "English uncomparable adjectives",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Mathematical analysis"
      ],
      "glosses": [
        "That is expressible as a countable union of compact sets."
      ],
      "links": [
        [
          "mathematical analysis",
          "mathematical analysis"
        ],
        [
          "countable",
          "countable"
        ],
        [
          "union",
          "union"
        ],
        [
          "compact",
          "compact"
        ]
      ],
      "raw_glosses": [
        "(mathematical analysis, of a set in a topological space) That is expressible as a countable union of compact sets."
      ],
      "raw_tags": [
        "of a set in a topological space"
      ],
      "tags": [
        "not-comparable"
      ],
      "topics": [
        "mathematical-analysis",
        "mathematics",
        "sciences"
      ]
    }
  ],
  "word": "σ-compact"
}