Machines
A machine is an enclosure which contains independent parts that exert force on each other to produce a desired function. This may be as simple as cogs in a drill press making holes or more complicated like employees working in a corporation to make profit.
It is the commonality of the parts which define the machine i.e. the majority of parts in a drill press do simple tasks which work together to make holes in things. Whereas in a corporation a collection of people work together to make profit. Machines always have inputs, a function and then based on their efficiency, a productive output (internality) and a waste output (externality).
Machine Theory
Hawkings[1], Musk[2], Gates[3], have all stated their fear of the potential existential threats we face with the development of AI. There are multiple reasons however it boils down to if you create something more intelligent that yourself it may find out some information which we do not know which might rationalise destroying human life. For instance, if an AI was tasked without hard written (ROM) specifying something along the lines of Issac Asimov''s three laws of robotics to protect biodiverse life on earth its first though would most probably kill the majority of humans.