Often you are at a terminal on your desktop and  you want to start a program but do not want to go through the menu.  You can type the command at the terminal and the program will start but your terminal can not be used till you close the program you started.

One option is to use the & option to run the program in the background, for example, firefox & starts Firefox and runs it in the background. This works well unless you close the terminal window which will close any programs you started with that terminal.  The solution is &disown.  By starting a program with &disown option the program starts but is not linked to the terminal session, so if the terminal closes the program started with the option will continue to run.  For example, firefox &disown will start Firefox but if the terminal window is closed firefox will continue to run.