A “Hello, World!” program is traditionally used to introduce novice programmers to a programming language.

Source: Wikipedia

Python example:

#!/usr/bin/env python
print('Hello, world!')

For more examples

Java: example

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

C# example:

using System;
class Program
{
    public static void Main(string[] args)
    {
        Console.WriteLine("Hello, World!");
    }
}

JavaScript example:

document.write('Hello, World!');

Ruby example:

puts "Hello, world!"

C example:

#include <stdio.h>
int main() {
    printf("Hello, World!");
    return 0;
}