Sushi only refers to the name of a popular Japanese cuisine, true or false? Wrong if you chose true. Sushi, huh? is the name (I wonder why it was named that way) of a portable application that downloads a Linux OS update on one computer with internet connection then installs it on a Linux box without an internet connection.
For example, I use it to download Ubuntu updates on my Windows computer at the office, then transfer those updates to a flash drive for installation on my Ubuntu box at home. It actually is a very useful utility especially if your only choice of internet connection is a pay as you go type or has a bandwidth cap.