Process Groups in PeopleSoft

The process groups are not stored in any setup table of its own.
They are stored in the table: PRCSDEFNGRP and PRCSJOBGRP where we store the process and job definitions.
If you take a look a look at the prompt for PRCSGRP field in those tables, it is a 'Prompt with no edit', so u can keep adding new Process groups on the fly, on process and job definition components (Page: Process Definition Options)

Significance of the process group:

They are linked with the user ID through a permission list. 

On the permission list setup, in the "Process tab", you can link the process groups.
This plays very important role in securing the processes and jobs in the system. Process groups to users are tied as below

Process Group ->Permission list -> Roles->User profiles

To find which permission lists have access to which process groups use the following query:

select * from PSAUTHPRCS order by CLASSID, PRCSGRP;

Below screens will show how the new process group is created and mapped through user profile.