Usability
Computers are everywhere! Washing machines, cars, phones, watches, space craft, ATMs. The list goes on. And then there is the obvious on-your-desk computer that if you believe the hype can make your life so much better with all the tasks it can do quickly and effeciently.
Regardless of the bit of technology, somehow the human user has to be able to tell it what to do, or at least give it a good amount of prodding in the right direction. There is usually some for of interface to allow the human to do this; a computer keyboard, mouse and screen, a remote control for a video recorder, the dashboard of a car.
Sadly these interfaces all to often fail the user and leave them with two hours of snooker when they wanted a documentary on the development of the seed drill. The minor usability failues can be little more than irritations or frustrating but when the failure results in catastrophy it is time to take note.
Usability is the art and science of making all these devices, literally and figuratively, less painful for us poor humans to use.