In some computer systems when a process creates another process, then the parent process and child process continue to be associated in certain ways. The child process can itself creates more processes that forms a process hierarchy.
In Unix system, a process group formed by a process and all of its children and further descendants.
Whenever a computer user sends a signal from the keyboard, that signal is then delivered to all the members of the process group that are currently associated with the keyboard.
Individually, each process can catch the signal, ignore the signal, or take the default action, windows systems doesn't have any concept of a process hierarchy.