"50K" meaning in English

{
  "etymology_templates": [
    {
      "args": {
        "1": "mul",
        "2": "50"
      },
      "expansion": "50",
      "name": "m"
    },
    {
      "args": {
        "1": "mul",
        "2": "-K",
        "3": "",
        "4": "-kilometer race"
      },
      "expansion": "-K (“-kilometer race”)",
      "name": "m"
    }
  ],
  "etymology_text": "From 50 + -K (“-kilometer race”).",
  "forms": [
    {
      "form": "50Ks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "50K (plural 50Ks)",
      "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": "Athletics",
          "orig": "en:Athletics",
          "parents": [
            "Sports",
            "Human activity",
            "Human behaviour",
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Fifty",
          "orig": "en:Fifty",
          "parents": [
            "Numbers",
            "All topics",
            "Terms by semantic function",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A 50 kilometer race."
      ],
      "id": "en-50K-en-noun-hMOkFiHy",
      "links": [
        [
          "athletics",
          "athletics"
        ],
        [
          "50",
          "50"
        ],
        [
          "kilometer",
          "kilometer"
        ],
        [
          "race",
          "race"
        ]
      ],
      "raw_glosses": [
        "(athletics) A 50 kilometer race."
      ],
      "topics": [
        "athletics",
        "hobbies",
        "lifestyle",
        "sports"
      ],
      "wikipedia": [
        "50 kilometres race walk"
      ]
    }
  ],
  "word": "50K"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "mul",
        "2": "50"
      },
      "expansion": "50",
      "name": "m"
    },
    {
      "args": {
        "1": "mul",
        "2": "-K",
        "3": "",
        "4": "-kilometer race"
      },
      "expansion": "-K (“-kilometer race”)",
      "name": "m"
    }
  ],
  "etymology_text": "From 50 + -K (“-kilometer race”).",
  "forms": [
    {
      "form": "50Ks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "50K (plural 50Ks)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English nouns",
        "English terms spelled with numbers",
        "English words without vowels",
        "en:Athletics",
        "en:Fifty"
      ],
      "glosses": [
        "A 50 kilometer race."
      ],
      "links": [
        [
          "athletics",
          "athletics"
        ],
        [
          "50",
          "50"
        ],
        [
          "kilometer",
          "kilometer"
        ],
        [
          "race",
          "race"
        ]
      ],
      "raw_glosses": [
        "(athletics) A 50 kilometer race."
      ],
      "topics": [
        "athletics",
        "hobbies",
        "lifestyle",
        "sports"
      ],
      "wikipedia": [
        "50 kilometres race walk"
      ]
    }
  ],
  "word": "50K"
}