Neuro-feedback, or Neuro Biofeedback is the process of measuring and monitoring the electrical activity in the brain, and is translated into "brain-waves". It's really just the electrical output of the human brain at different states of conscious levels, and can be useful in diagnosing some conditions or in the case of epilepsy. Neuro-biofeedback requires the attachment of several small sensors to the cranium and then viewing the recorded levels of brain activity on a computer screen.
By doing this you can eventually learn how to modify your mental state, and is so doing you can modify your energy and mood levels, along with brain functionality and activity. The kinds of brain-waves (signal pulses from the brain) are as follows: 14-24hz are called Beta Waves, and are detected with high level of mental activity which is used during problem solving and decision making. 12-14htz are called SMR waves, and are detected when the mind is at attention, storing and sequencing information that is later used, and can also be seen as optimal for when playing sports. 8-12htz are called Alpha waves, it is usually found in an alert state of mind, but at rest. 4-8htz is called theta waves, and they are found at a state of mind associated with mental creativity and inspiration, when an inventor gets to thinking and gets his idea, or a painter gets the idea for a painting. Anything at 4htz or less is called Delta waves, and they are found during deep relaxation.
Neuro Biofeedback and Neuro feedback are also used in the treatment of diseases and disorders - like ADHD and ADD, along with depression and other mental disorders (OCD's). Modern mainstream medicine monitors brain waves during conative exercises to determine the efficency of one's mind after an accident or to see what state of mind someone is in.