"fencepost error" meaning in English

{
  "forms": [
    {
      "form": "fencepost errors",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "fencepost error (plural fencepost errors)",
      "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": "Programming",
          "orig": "en:Programming",
          "parents": [
            "Computing",
            "Software engineering",
            "Technology",
            "Computer science",
            "Engineering",
            "Software",
            "All topics",
            "Sciences",
            "Applied sciences",
            "Media",
            "Fundamental",
            "Communication"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "An off-by-one error arising from the fencepost problem."
      ],
      "id": "en-fencepost_error-en-noun-4I~vDjXW",
      "links": [
        [
          "programming",
          "programming#Noun"
        ],
        [
          "off-by-one error",
          "off-by-one error"
        ],
        [
          "fencepost problem",
          "fencepost problem"
        ]
      ],
      "raw_glosses": [
        "(programming) An off-by-one error arising from the fencepost problem."
      ],
      "topics": [
        "computing",
        "engineering",
        "mathematics",
        "natural-sciences",
        "physical-sciences",
        "programming",
        "sciences"
      ]
    }
  ],
  "word": "fencepost error"
}

{
  "forms": [
    {
      "form": "fencepost errors",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "fencepost error (plural fencepost errors)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "en:Programming"
      ],
      "glosses": [
        "An off-by-one error arising from the fencepost problem."
      ],
      "links": [
        [
          "programming",
          "programming#Noun"
        ],
        [
          "off-by-one error",
          "off-by-one error"
        ],
        [
          "fencepost problem",
          "fencepost problem"
        ]
      ],
      "raw_glosses": [
        "(programming) An off-by-one error arising from the fencepost problem."
      ],
      "topics": [
        "computing",
        "engineering",
        "mathematics",
        "natural-sciences",
        "physical-sciences",
        "programming",
        "sciences"
      ]
    }
  ],
  "word": "fencepost error"
}