This code system http://hl7.org/fhir/insuranceplan-applicability defines the following codes:

Code	Display	Definition
in-network	In Network	Provider is contracted with the health insurance company to provide services to plan members for specific pre-negotiated rates
out-of-network	Out of Network	Provider is not contracted with the health insurance company to provide services to plan members for specific pre-negotiated rates
other	Other	Other applicability