What is brain waves ?
Please refer to this excellent description below

Please note : Below article is referenced from wellandgood web site (https://www.wellandgood.com/good-advice/brainwaves-biohack-sleep-health-focus)

"The 5 types of brainwaves
Now here’s where it gets fun: Brainwaves are grouped into five distinct categories, each of which is associated with a very specific type of task and mental state.

The most high-frequency—and, some may say, high-vibe—of the bunch are gamma waves. “Gamma waves are often associated with insight, peak focus, and expanded consciousness,” says Winters. “These waves are generated when the brain is learning new information, sharply concentrating, or storing memories.” She adds that this “hyper-focused, tranquil attention” is characteristic of Zen meditators and master musicians.

A step down are beta waves, which is what most of us experience most of the time in our always-on society. “Their upside is that they allow us to concentrate hard on tasks at hand—and they’re critical when we read, write, and socialize,” says Winters. (It’s the frequency of the hustle, basically.) “The downside of beta waves is that they can zap our energy and reduce emotional awareness and creativity.”

Once we get home at the end of the day, if we’re lucky, we shift into a relaxed, reflective alpha wave pattern. “If you daydream, wind down for bed, or sit down with a good book, your brain is likely in an alpha state,” says Winters. On the other hand, if your brain has trouble shifting from beta to alpha—a stress-induced phenomenon called “alpha blocking”—you could suffer from insomnia, anxiety, or obsessive-compulsive symptoms, says Winters.

Finally, once you fall asleep, you experience theta waves (the ones associated with dreaming) and delta waves (which promote deep, restorative, dreamless slumber.) Interestingly, theta waves are also linked with being in that elusive, hypnotic flow state associated with peak performance, as well as the autopilot mode we shift into when we’re doing something we’ve done a million times before, like driving home from work on a familiar route. “[People can] have flashes of insight or bursts of creativity when in these flow states because their behaviors are often so automatic that they can mentally disengage and just be,” explains Winters. So that explains why I have all my best ideas in the shower… "