The legendary text editor for Unix invented by Bill Joy in 1976. It has two modes: Insert and Command. It is the living hell for people new to Unix and they want to get out of it as soon as possible to end the nightmare.

ESC is the key to switch back to command mode. In command mode, the keys H, J, K, L can be used to move the cursor:

H: Left

J: Down

K: Up

L: Right

vi is short for visual.