From Wikipedia :

“A “Hello World” program is a computer program which prints out “Hello World!” on a display device. It is used in many introductory tutorials for teaching a programming language. Such a program is typically one of the simplest programs possible in most computer languages. It is often considered to be tradition among programmers for people attempting to learn a new programming language to write a “Hello World!” program as one of the first steps of learning that particular language. Some are surprisingly complex, especially in some graphical user interface (GUI) contexts, but most are very simple, especially those which rely heavily on a particular command line interpreter (“shell”) to perform the actual output. In an embedded system, the text may be sent to a liquid crystal display (LCD), or the message may be substituted by some other appropriate signal, such as an LED being turned on.”

http://en.wikipedia.org/wiki/Hello_world_program