Neurofeedback is brain wave biofeedback (EEG biofeedback). The electrical activity of the brain is read with special sensors and recorded by the computer. Without the computer reading our brain signals we don't know what our brain activity is -- and so we aren't able to change it. But neurofeedback gives us that information.
You learn to change brain wave patterns by playing computer "games." For example, you make a fish swim to the bottom of the ocean if you focus and concentrate. As soon as you lose focus, the fish goes to the top. This feedback allows you to experience exactly what it is like to focus. With repeated practice, focus becomes automatic.
With neurofeedback, you learn to change patterns of brain waves through operant conditioning. Research shows that some neurological and psychological disorders can be characterized by distinctive EEG patterns and that neurofeedback may help clients to change those patterns. (Masterpasqua and Healey, 2003, Neurofeedback in Psychological Practice.)
There are a number of brain waves - the chart shows the most common ones.