Thank you for you query.
Client is the first parameter of the Main subroutine in every Formativ applet. Here is a quote from the Formativ Programmers Guide:
This parameter represents the state of the GroupWise client at the time your applet was executed. It is the same as the GroupWise C3PO ClientState Object as documented in the GroupWise C3PO documentation.
You will find more information in the Programmers Guide on the properties and methods of Client.ClientState.
I hope this helps.