"metasyntactic variable" meaning in English

{
  "forms": [
    {
      "form": "metasyntactic variables",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "metasyntactic variable (plural metasyntactic variables)",
      "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"
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          "source": "w"
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          "name": "Terms with Swedish translations",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Programming",
          "orig": "en:Programming",
          "parents": [
            "Computing",
            "Software engineering",
            "Technology",
            "Computer science",
            "Engineering",
            "Software",
            "All topics",
            "Sciences",
            "Applied sciences",
            "Media",
            "Fundamental",
            "Communication"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "Use metasyntactic variables like foo and bar when you need a name but the particular name doesn't matter."
        }
      ],
      "glosses": [
        "A conventional variable name used for an unspecified entity whose exact nature depends on context."
      ],
      "id": "en-metasyntactic_variable-en-noun-T9c3Bw~C",
      "links": [
        [
          "programming",
          "programming#Noun"
        ],
        [
          "variable",
          "variable"
        ],
        [
          "unspecified",
          "unspecified"
        ],
        [
          "context",
          "context"
        ]
      ],
      "raw_glosses": [
        "(chiefly programming) A conventional variable name used for an unspecified entity whose exact nature depends on context."
      ],
      "related": [
        {
          "word": "foo"
        },
        {
          "word": "bar"
        },
        {
          "word": "baz"
        },
        {
          "word": "quux"
        },
        {
          "word": "fnord"
        },
        {
          "word": "fum"
        },
        {
          "word": "shme"
        },
        {
          "word": "zot"
        },
        {
          "word": "foobar"
        },
        {
          "word": "fred"
        },
        {
          "word": "wibble"
        },
        {
          "word": "derp"
        }
      ],
      "topics": [
        "computing",
        "engineering",
        "mathematics",
        "natural-sciences",
        "physical-sciences",
        "programming",
        "sciences"
      ],
      "translations": [
        {
          "code": "fi",
          "lang": "Finnish",
          "sense": "in computing",
          "word": "metasyntaktinen muuttuja"
        },
        {
          "code": "sv",
          "lang": "Swedish",
          "sense": "in computing",
          "word": "metavariabel"
        }
      ],
      "wikipedia": [
        "metasyntactic variable"
      ]
    }
  ],
  "word": "metasyntactic variable"
}

{
  "forms": [
    {
      "form": "metasyntactic variables",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "metasyntactic variable (plural metasyntactic variables)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "foo"
    },
    {
      "word": "bar"
    },
    {
      "word": "baz"
    },
    {
      "word": "quux"
    },
    {
      "word": "fnord"
    },
    {
      "word": "fum"
    },
    {
      "word": "shme"
    },
    {
      "word": "zot"
    },
    {
      "word": "foobar"
    },
    {
      "word": "fred"
    },
    {
      "word": "wibble"
    },
    {
      "word": "derp"
    }
  ],
  "senses": [
    {
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        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English placeholder terms",
        "Entries with translation boxes",
        "Pages with 1 entry",
        "Pages with entries",
        "Terms with Finnish translations",
        "Terms with Swedish translations",
        "en:Programming"
      ],
      "examples": [
        {
          "text": "Use metasyntactic variables like foo and bar when you need a name but the particular name doesn't matter."
        }
      ],
      "glosses": [
        "A conventional variable name used for an unspecified entity whose exact nature depends on context."
      ],
      "links": [
        [
          "programming",
          "programming#Noun"
        ],
        [
          "variable",
          "variable"
        ],
        [
          "unspecified",
          "unspecified"
        ],
        [
          "context",
          "context"
        ]
      ],
      "raw_glosses": [
        "(chiefly programming) A conventional variable name used for an unspecified entity whose exact nature depends on context."
      ],
      "topics": [
        "computing",
        "engineering",
        "mathematics",
        "natural-sciences",
        "physical-sciences",
        "programming",
        "sciences"
      ],
      "wikipedia": [
        "metasyntactic variable"
      ]
    }
  ],
  "translations": [
    {
      "code": "fi",
      "lang": "Finnish",
      "sense": "in computing",
      "word": "metasyntaktinen muuttuja"
    },
    {
      "code": "sv",
      "lang": "Swedish",
      "sense": "in computing",
      "word": "metavariabel"
    }
  ],
  "word": "metasyntactic variable"
}