What is the APPX Process Stack?

Running an APPX application consists of a series of processes calling each other. For example, the Main Menu might call a submenu, which might call a JOB process, which might call an INPUT, which might call a child INPUT process, etc.

The list of current processes that have called each other is called a "Process Stack". This is a particular 'drill down' within a Process Family, or Process Tree.