From the reading of the text, it’s a serialized job queue for arbitrary commands submitted from the command line. It’s the equivalent of “cmd1 & cmd2 & cmd3” ex

From the reading of the text, it’s a serialized job queue for arbitrary commands submitted from the command line. It’s the equivalent of “cmd1 & cmd2 & cmd3” except all are put to the background and will be run serially one after another. And new command is automatically added to the end.