Definitions for "Service principal name"
(SPN) The name by which a client uniquely identifies an instance of a service. If you install multiple instances of a service on computers throughout a forest, each instance must have its own SPN. A given service instance can have multiple SPNs if there are multiple names that clients might use for authentication
a principal name that authorizes a client to use a particular service, including the specific application server machine the service will access and the realm name
a principal name that authorizes an application server to use a particular service