API Playground - C#

HomeController.cs

[HttpPost]
public async Task<IActionResult> CSharp(Code code)
{
    string output = code.csx;

    var apiURL = "https://www.microsoft.com/net/api/code";

    using (var client = new HttpClient())
    {
        HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, new Uri(apiURL));
        request.Headers.Add("Referer", "https://www.microsoft.com/net");
        var codeSnippet = code.csx;

        var codeInput = new CodeRequest { language = "csharp", captureStats = false, sources = new string[1] };
        codeInput.sources[0] = codeSnippet;

        var request_content = JsonConvert.SerializeObject(codeInput);
        request.Content = new StringContent(request_content, Encoding.UTF8, "application/json");
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        HttpResponseMessage response = await client.SendAsync(request);

        var responseString = await response.Content.ReadAsStringAsync();
        var codeOutput = JsonConvert.DeserializeObject<CodeResponse>(responseString);
        code.output = codeOutput.Output[0];
    }

    return View(code);
}

what is res?