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.

<wsdl:definitions name="Service1" targetNamespace="http://tempuri.org/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://schemas.xmlsoap.org/wsdl/soap12/" xmlns:tns="http://tempuri.org/" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:wsp="http://schemas.xmlsoap.org/ws/2004/09/policy" xmlns:wsap="http://schemas.xmlsoap.org/ws/2004/08/addressing/policy" xmlns:wsaw="http://www.w3.org/2006/05/addressing/wsdl" xmlns:msc="http://schemas.microsoft.com/ws/2005/12/wsdl/contract" xmlns:wsa10="http://www.w3.org/2005/08/addressing" xmlns:wsx="http://schemas.xmlsoap.org/ws/2004/09/mex" xmlns:wsam="http://www.w3.org/2007/05/addressing/metadata">
  <wsdl:types>
    <xsd:schema targetNamespace="http://tempuri.org/Imports">
      <xsd:import schemaLocation="http://localhost:63720/Service1.svc?xsd=xsd0" namespace="http://tempuri.org/"/>
    </xsd:schema>
  </wsdl:types>
  <wsdl:message name="IService1_DoWork_InputMessage">
    <wsdl:part name="parameters" element="tns:DoWork"/>
  </wsdl:message>
  <wsdl:message name="IService1_DoWork_OutputMessage">
    <wsdl:part name="parameters" element="tns:DoWorkResponse"/>
  </wsdl:message>
  <wsdl:portType name="IService1">
    <wsdl:operation name="DoWork">
      <wsdl:input wsaw:Action="http://tempuri.org/IService1/DoWork" message="tns:IService1_DoWork_InputMessage"/>
      <wsdl:output wsaw:Action="http://tempuri.org/IService1/DoWorkResponse" message="tns:IService1_DoWork_OutputMessage"/>
    </wsdl:operation>
  </wsdl:portType>
  <wsdl:binding name="BasicHttpBinding_IService1" type="tns:IService1">
    <soap:binding transport="http://schemas.xmlsoap.org/soap/http"/>
    <wsdl:operation name="DoWork">
      <soap:operation soapAction="http://tempuri.org/IService1/DoWork" style="document"/>
      <wsdl:input>
        <soap:body use="literal"/>
      </wsdl:input>
      <wsdl:output>
        <soap:body use="literal"/>
      </wsdl:output>
    </wsdl:operation>
  </wsdl:binding>
  <wsdl:service name="Service1">
    <wsdl:port name="BasicHttpBinding_IService1" binding="tns:BasicHttpBinding_IService1">
      <soap:address location="http://localhost:63720/Service1.svc"/>
    </wsdl:port>
  </wsdl:service>
</wsdl:definitions>

Tip: Use a constant to ensure consistency

I like to use a constant to provide a consistent namespace across my services

public class Constants
{
    // Ensures consistency in the namespace declarations across services
    public const string Namespace = "http://contoso.com/services/";
}

How to eliminate tempuri.org from WCF Services WSDL

Step 1: Declare a namespace on your service contract

The namespace can be anything.  People typically use a URI of some form but it does not have to point to an actual web page.  Often people will use a version identifier in the namsepace but there are no rules about what you should do.

// Eliminate tempuri.org from the contract
// If you don't want to us a constant, put the URI here
// [ServiceContract(Namespace = "http://contoso.com/services")]
[ServiceContract(Namespace = Constants.Namespace)]
public interface IService1
{
    [OperationContract]
    void DoWork();
}

Step 2: Declare a namespace on your service

The service namespace is added with a ServiceBehavior attribute.  Using the constant ensures that the namespace is the same for the contract and the service.

// If you don't want to us a constant, put the URI here
// [ServiceBehavior(Namespace = "http://contoso.com/services")]
[ServiceBehavior(Namespace = Constants.Namespace)]
public class Service1 : IService1
{
    public void DoWork()
    {
    }
}

Step 3: Set the binding namespace

<system.serviceModel>
    <services>
      <service name="EliminateTempUri.Service1">
        <!-- Use a bindingNamespace to eliminate tempuri.org -->
        <endpoint address=""
                  binding ="basicHttpBinding"
                  bindingNamespace="http://contoso.com/services"
                  contract="EliminateTempUri.IService1"
        />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="">
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="false" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
  </system.serviceModel>