ThreadedEvent is a Boolean property that indicates if data handling and protocol suboption negotiations are executed in the context of the TelnetThread or synchronized to the main VCL thread for the application. Data handling and protocol negotiations are performed using the OnDataAvailable and the OnTelnetCommand event handlers. 

When ThreadedEvent contains True, event handlers notifications are executed in the context of the TelnetThread. 

When ThreadedEvent contains False, event handler notifications are synchronized to the main VCL thread. Set ThreadedEvent to False when the event handlers are not thread-safe or require access to classes and routines available only in the main VCL thread. 

The default value for ThreadedEvent is False.

TIdTelnet.TelnetThread 

TIdTelnet.OnDataAvailable 

TIdTelnet.OnTelnetCommand