"Hello World" is the first program one usually writes when learning a new programming language. Having first been mentioned in Brian Kernighan's tutorial to the B programming language, it became widely known through Kernighan & Ritchie's 1978 book that introduced "The C Programming Language", where it read like this:

main() {
printf("hello, world\n");
}

Since then, Hello World has been implemented in just about every programming language on the planet. This collection includes 571 Hello World programs in as many more-or-less well known programming languages, plus 76 human languages.