This code system http://hl7.org/fhir/namingsystem-type defines the following codes:

CodeDisplayDefinition
codesystemCode SystemThe naming system is used to define concepts and symbols to represent those concepts; e.g. UCUM, LOINC, NDC code, local lab codes, etc.
identifierIdentifierThe naming system is used to manage identifiers (e.g. license numbers, order numbers, etc.).
rootRootThe naming system is used as the root for other identifiers and naming systems.