Brain waves are electrical impulses in the brain that result from the activity of neurons. They can be measured using an electroencephalogram (EEG) and are categorized into different types based on their frequency, including delta, theta, alpha, beta, and gamma waves. Each type of brain wave is associated with different states of consciousness, such as sleep, relaxation, or alertness. The frequency of brain waves is measured in hertz (Hz), with delta waves being the slowest (0.5-4 Hz) and gamma waves being the fastest (30 Hz and above). Understanding brain waves can help researchers study various mental states and conditions, including sleep disorders, anxiety, and attention deficit hyperactivity disorder (ADHD).