Hello World!
"Hello World" is the first thing that must be printed as a tradition when someone tries his/her first code in a specific programming language. It means your first code is successfully working. Doctors are tapping slapping babies' asses {less crude="bottom"}* when they are born to check if the baby is alive or dead. Imagine this in the same way, when you run your code: it says "Hello World" instead of crying.
*"We usually say that the doctor slaps the baby's bottom. Saying "ass" in the context of buttocks is familiar and little crude or mildly vulgar.