vi, pronounced by using each letter (vee-aye), is a widely-used and popular UNIX-based text editor. Like most UNIX system interfaces and other text editors, it lets you control the system by using the keyboard rather than a combination of mouse selections and keystrokes. The succinctness of the interface makes it highly useful for people who work at a computer all day, especially programmers entering or manipulating language statements. vi was invented before and is a popular alternative to Emacs, which is said to be more capable, more complicated, and somewhat slower. Like Emacs, vi is most commonly used for entering and editing program language statements and for writing short notes including e-mail. vi usually comes as part of any UNIX-based system.
vi is not to be confused with a word processor, an application that may be less efficient than vi for programmers but easier-to-use for non-programmers.