question about ApplicationInfo object when instantiating new service

In the sample applications there is an application Id that gets set on the service.  Can anyone tell me what that refers to in Netsuite.  It isn't required but if it is accessible it may be useful for tracking webservice activity.  I haven't been able to find reference to it in the documentation.  I have included the code below.

Thanks

NetSuiteService service = new NetSuiteService();

// Adding application id to track the use of the application
ApplicationInfo appInfo = new ApplicationInfo();
appInfo.applicationId = applicationId;
service.applicationInfo = appInfo;