tempuri.org is the default namespace applied to WCF Services and Workflow Services. You can and should specify your service namespace.
It is recommended that you explicitly specify a name and namespace for the service contract, and an action for each operation to avoid using "http://tempuri.org" and to prevent interface and method names from being exposed in the service’s contract
MSDN Library - Service Contract Versioning
Where is tempuri.org in the WSDL?
If you browse the service WSDL you will see tempuri.org all over the place. Here is a default WCF service WSDL.
Read more: The .NET Endpoint