Connect is an overridden procedure in TIdTelnet used to connect the TELNET client to a remote host computer identified by the Host and Port properties. 

Connect calls the inherited method to open the socket connection for the client, and creates the TIdTelnetReadThread instance used to read data from the socket connection. If the client is successfully connected, the TelnetThread property is initialized. 

If an error occurs when opening the socket connection and/or instantiating the TelnetThread, the connection is closed and an exception is raised. The connection is closed by calling Disconnect using the immediate disconnection argument. The exception raised is a EIdTelnetClientConnectError class instance with the message RSNoCreateListeningThread. 

Use Disconnect to close the TELNET client.

TIdTelnet.Disconnect 

TIdTelnet.TelnetThread 

EIdTelnetClientConnectError 

RSNoCreateListeningThread