It’s pretty common to issue commands in a Linux terminal that take a little while to complete. Instead of sitting and waiting for the program or process to complete, you can issue the alert command so you know when it completes.
For example, if you issue the command sleep 5; alert, your terminal will run the sleep program for 5 seconds and then you will receive a pop up alert on your desktop. This lets you know that the process has finished. Here it is in action:
This is great for long-running dd commands or installation of new programs that take a while. As an aside, I did have to install libnotify-bin for this to work properly.