What’s the difference between Properties and Fields in Elasticsearch documents

Question

What is the difference of properties and Fields? when creating a mapping I have the possibility to define a value with both; What and When I should use each one?

Below a document from Elasticsearch whose mapping was dynamically generated by the tool itself:

{
  "_index": "top-fornecedores-logs-2021.03.03",
  "_type": "_doc",
  "_id": "Sd959XcBR7kZ5_B9MCc9",
  "_version": 1,
  "_score": null,
  "_source": {
    "origin": "App.Api.Worker",
    "@type": "amqp",
    "date": "2021-03-02 21:24:55.7716",
    "@source": "nlog://DESKTOP-F8BDSSI/App.Log.Gerencia.RelatorioGerencialPDFService",
    "@tags": [],
    "level": "ERROR",
    "type": "App.Log",
    "logger": "App.Log.Gerencia.RelatorioGerencialPDFService",
    "machineName": "DESKTOP-F8BDSSI",
    "exception": "System.ApplicationException: Error in the application.",
    "@message": "02/03/2021 21:24:55 TESTE PDF",
    "@fields": {
      "exception": {
        "RemoteStackTraceString": null,
        "WatsonBuckets": null,
        "HResult": -2146232832,
        "StackTraceString": null,
        "Data": null,
        "InnerException": null,
        "RemoteStackIndex": 0,
        "ClassName": "System.ApplicationException",
        "Source": null,
        "Message": "Error in the application.",
        "HelpURL": null,
        "ExceptionMethod": null
      }
    },
    "@timestamp": "2021-03-03T00:24:55.771Z",
    "@version": "1"
  },
  "fields": {
    "@timestamp": [
      "2021-03-03T00:24:55.771Z"
    ]
  },
  "highlight": {
    "level": [
      "@kibana-highlighted-field@ERROR@/kibana-highlighted-field@"
    ]
  },
  "sort": [
    1614731095771
  ]
}