A “Hello world” program is a computer program that prints out “Hello world” on a display device. It is typically one of the simplest programs possible in most programming languages. Therefore, by tradition, it is often the first program taught in a beginning class on a particular language. It is also used to illustrate the most basic syntax of a programming language.

Most of these programs are very simple, especially those that rely on a command-line interpreter (shell) to perform the actual output. However, they can be surprisingly complex, especially when writing the program for graphical user interface. 

When programming an embedded system, the text may be sent to a liquid crystal display. In a device that does not display text, a simple program to produce a signal, such as turning on an LED, may be substituted for “Hello world” as the introductory program.