The exit status, commonly also referred to as exit codes or return codes, is the way Bash communicates the successful or unsuccessful termination of a process to its parent. In Bash, all processes are forked from the shell that calls them. The following diagram illustrates this:
When a command runs, such as ps -f in the preceding diagram, the current shell is copied (including the environment variables!), and the command runs in the copy, called the fork. After the command/process is done, it terminates the fork and returns the exit status to the shell that it was initially forked from (which, in the case of an interactive session, ...
