This is a HL7 FHIR server, and as you appear to be accessing this page from a web browser you are seeing a HTML version of the requested resource(s). You can also access this URL from a FHIR client as a ReSTful API call. For more details please see the HL7 FHIR specification.
{
  "resourceType": "CodeSystem",
  "id": "CareConnect-NHSNumberVerificationStatus-1",
  "text": {
    "status": "generated"
  },
  "extension": [
    {
      "url": "http://hl7.org/fhir/StructureDefinition/codesystem-sourceReference",
      "valueUri": "http://www.datadictionary.nhs.uk/data_dictionary/data_field_notes/n/nhs/nhs_number_status_indicator_code_de.asp?shownav=1"
    }
  ],
  "url": "https://fhir.hl7.org.uk/STU3/CodeSystem/CareConnect-NHSNumberVerificationStatus-1",
  "version": "1.1.0",
  "name": "Care Connect NHS Number Verification Status",
  "status": "draft",
  "date": "2018-11-02T00:00:00+00:00",
  "publisher": "HL7 UK",
  "description": "A CodeSystem that identifies the trace status of the NHS number. This CodeSystem is comprised of codes from the NHS Data Model and Dictionary: NHS Number Status Indicator Code.",
  "copyright": "Copyright © 2016 HL7 UK",
  "caseSensitive": true,
  "content": "complete",
  "concept": [
    {
      "code": "01",
      "display": "Number present and verified"
    },
    {
      "code": "02",
      "display": "Number present but not traced"
    },
    {
      "code": "03",
      "display": "Trace required"
    },
    {
      "code": "04",
      "display": "Trace attempted - No match or multiple match found"
    },
    {
      "code": "05",
      "display": "Trace needs to be resolved - (NHS number or patient detail conflict)"
    },
    {
      "code": "06",
      "display": "Trace in progress"
    },
    {
      "code": "07",
      "display": "Number not present and trace not required"
    },
    {
      "code": "08",
      "display": "Trace postponed (baby under six weeks old)"
    }
  ]
}