OnRun is a TIdContextRun event handler property that represents the event handler signalled to execute the task for the client session context. 

The session context is passed as an argument to the event handler during execution. OnRun is normally assigned a procedure in the server that triggers the OnExecute loop for the TCP server. Listener threads in TIdTCPServer assign procedures for the OnBefore, OnRun, and OnAfterRun event handlers that trigger the OnConnect, OnExecute, and OnDisconnect event handlers (respectively).

TIdContextRun 

TIdListenerThread 

TIdTCPServer.OnConnect 

TIdTCPServer.OnExecute 

TIdTCPServer.OnDisconnect