The Halting Problem is the problem of deciding whether a computer program will finish or go on forever. It is an example of a decision problem, a problem where you have a yes or no and it’s one of the key results in the theory of computation. It’s easy to formulate and impossible to solve using the Turing Machine. And what is important about the Halting Problem was that inside it there was a formal definition of what a computer is and what a piece of software or computer program was.