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": "ConceptMap",
  "id": "CareConnect-MaritalStatus-1",
  "url": "https://fhir.hl7.org.uk/STU3/ConceptMap/CareConnect-MaritalStatus-1",
  "version": "1.0.0",
  "name": "Concept Map - Care Connect Marital Status",
  "status": "active",
  "date": "2017-08-01T00:00:00+00:00",
  "publisher": "HL7 UK",
  "description": "A Concept Map from ValueSet Marital Status to NHS Data Dictionary Person Marital Status to aid interpretation.",
  "copyright": "Copyright © 2016 HL7 UK",
  "sourceReference": {
    "reference": "https://fhir.hl7.org.uk/STU3/ValueSet/CareConnect-MaritalStatus-1"
  },
  "targetReference": {
    "reference": "https://fhir.hl7.org.uk/STU3/ValueSet/CareConnect-NHSDataDictionary-PersonMaritalStatus-1"
  },
  "group": [
    {
      "source": "http://hl7.org/fhir/v3/MaritalStatus",
      "target": "https://fhir.hl7.org.uk/STU3/CodeSystem/CareConnect-NHSDataDictionary-PersonMaritalStatus-1",
      "element": [
        {
          "code": "U",
          "display": "unmarried",
          "target": [
            {
              "code": "S",
              "display": "Single",
              "equivalence": "equivalent"
            }
          ]
        },
        {
          "code": "D",
          "display": "Divorced",
          "target": [
            {
              "code": "D",
              "display": "Divorced/Person whose Civil Partnership has been dissolved",
              "equivalence": "equivalent"
            }
          ]
        },
        {
          "code": "L",
          "display": "Legally Separated",
          "target": [
            {
              "code": "P",
              "display": "Separated",
              "equivalence": "equivalent"
            }
          ]
        },
        {
          "code": "M",
          "display": "Married",
          "target": [
            {
              "code": "M",
              "display": "Married/Civil Partner",
              "equivalence": "equivalent"
            }
          ]
        },
        {
          "code": "S",
          "display": "Never Married",
          "target": [
            {
              "code": "S",
              "display": "Single",
              "equivalence": "equivalent"
            }
          ]
        },
        {
          "code": "W",
          "display": "Widowed",
          "target": [
            {
              "code": "W",
              "display": "Widowed/Surviving Civil Partner",
              "equivalence": "equivalent"
            }
          ]
        }
      ]
    },
    {
      "source": "http://hl7.org/fhir/v3/NullFlavor",
      "target": "https://fhir.hl7.org.uk/STU3/CodeSystem/CareConnect-NHSDataDictionary-PersonMaritalStatus-1",
      "element": [
        {
          "code": "UNK",
          "display": "unknown",
          "target": [
            {
              "code": "N",
              "display": "Not disclosed",
              "equivalence": "equivalent"
            }
          ]
        }
      ]
    }
  ]
}