Monotasking, also known as single-tasking, is the practice of dedicating oneself to a given task and minimizing potential interruptions until the task is completed or a significant period of time has elapsed.
Monotasking contrasts with multitasking, which is the ability to divide one's focus among multiple tasks. Most knowledge workers consider themselves to be multitasking and a large proportion believe themselves to be supertaskers, who are able to handle more than two tasks at any given time. The capacity to multitask is highly valued in many businesses. However, most research into multitasking fails to support its effectiveness and even the human capacity to do it.
According to Earl Miller, a professor of neuroscience at MIT, people only think they're multitasking. What they're actually doing is switching rapidly between tasks and there's cognitive stress added with every switch, which accumulates and can eventually lead to fatigue, overload and burnout. Furthermore, research shows that the attempt to multitask actually hampers productivity and that people who consider themselves multitaskers or supertaskers perform more poorly than other workers.
See Paolo Cardini's brief TED talk, Forget multitasking, try monotasking: