Your brain is made up of billions of brain cells called neurons, which use electricity to communicate with each other. The combination of millions of neurons sending signals at once produces an enormous amount of electrical activity in the brain, which can be detected using sensitive medical equipment (such as an EEG), measuring electricity levels over areas of the scalp.
The combination of electrical activity of the brain is commonly called a BrainWave pattern, because of its cyclic, “wave-like” nature.