The OriginatingOSUser property of the LogMessage2 object is a Read-Only string that represents the user sending a message as determined by an application. The MessageLog2.SendLogMessage method will automatically add the ProcessOSUser to each log message. However in some cases, such as an application server, the user associated with the application's process may not be the user that the message pertains to. In this case the application may choose to use the OriginatingOSUser property of a message to clearly define the sender or related user of the message.
The object placeholder is an object expression that evaluates to a LogMessage2 object.