Figure (1.a): The wait() system call blocks the caller until one of its child processes terminates. If the caller doesn’t have any child processes, wait returns immediately without blocking the caller. Using wait the parent can obtain the exit status of the terminated child.
Figure (1.b): The parent process creates a child process and waits until the child finishes its execution.
Figure (1.c): The parent process creates a child and starts executing concurrently with its children. UNIX uses vfork() function to do this job.
Reference: http://www.it.uu.se/education/course/homepage/os/vt18/module-2/process-management/
