"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": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms containing italics",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms written in multiple scripts",
          "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": "Mathematical analysis",
          "orig": "en:Mathematical analysis",
          "parents": [],
          "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"
}