Brainwave entrainment is a colloquialism for such 'neural entrainment', which is a term used to denote the way in which the aggregate frequency of oscillations produced by the synchronous electrical activity in ensembles of cortical neurons can adjust to synchronize with the periodic vibration of an external stimuli, such as a sustained acoustic frequency perceived as pitch, a regularly repeating pattern of intermittent sounds, perceived as rhythm, or of a regularly rhythmically intermittent flashing light.
I have many new age, meditation, classical and jazz cds that I use for relaxation. This Steven Halpern cd is now my favorite one. I can listen to it for hours on end while I read, write, use the computer, or just veg out on the couch at home or lounge at the pool. I especially love the tracks with the ocean wave sounds mixed in with the electronic music. I definitely am in the theta brain wave state while listening to it, and I know that's the reason it is so much more soothing than any other cd that I own. It is really great for eliminating any anger or anxiety that I may be feeling. I believe it's also improving my sleep. I give this cd the highest possible recommendation!

(Shannahoff-Khalsa, 1991; Webb & Dube, 1981). These naturally occurring shifts may underlie the anecdotal reports of fluctuations in the effectiveness of binaural beats. External factors are also thought to play roles in mediating the effects of binaural beats (Owens & Atwater, 1995). The perception of a binaural beat is, for example, said to be heightened by the addition of white noise to the carrier signal (Oster, 1973), so white noise is often used as background. "Music, relaxation exercises, guided imagery, and verbal suggestion have all been used to enhance the state-changing effects of the binaural beat" (Owens & Atwater, 1995). Other practices such as humming, toning, breathing exercises, autogenic training, and/or biofeedback can also be used to interrupt the homeostasis of resistant subjects (Tart, 1975).
Today, EEG machines are used for diagnosing epilepsy and sleep disorders, for determining dosages for anesthesia, and measuring the brain activity of people in comas or suffering from brain trauma. EEG machines also continue to play a role in researching and understanding brainwave entrainment and developing new and better methods for delivering the benefits of this form of brainwave modification. 
A 2008 study at Hofstra University played two different binaural beats and a control sound (a babbling brook) to patients with high blood pressure. There was no difference between the groups. In one small study from Japan that was published in the Journal of Neurophysiology in 2006, they played various binaural beats to nine subjects, and observed the resulting EEGs. They found great variability in the results. Their conclusion was that listening to binaural beats can produce activity on the human cerebral cortex, however the cause was more likely a conscious auditory reaction and was not correlated to the frequency of the binaural beat. However, a 2005 study published in Clinical Neurophysiology found that they were able to induce a desired frequency in the EEG matching the phantom beat frequency encoded in a binaural beat, however this was with a single subject and was neither blinded nor controlled.
Thanks to e-mail, cell phones, and BlackBerrys, it seems like your job never ends. The increasingly blurry boundaries between work and home life leave us with less downtime than ever before (and in some cases, no downtime!). Advances in technology are a leading source of chronic stress, putting many of us in a constant state of alert. Not to mention the effect it has on family ties. A recent study published in the Journal of Marriage and Family found a link between the use of cell phones and pagers at home and increased stress, which spills over into family life. To make technology work for you, screen calls with caller ID or, better yet, limit your cell phone and e-mail use to working hours only. Can't kick the BlackBerry habit? Set a regular time you'll check it in the evening (say, after dinner), so you're not constantly disrupting home life to keep tabs on work. (The one exception: using your device to breathe with this anxiety-reducing GIF.)
They are not beyond what is “normal” but for most of us they are outside of what is “typical”. Whether we consciously seek them or not, somewhere in the back of our minds we hold beliefs that because meditation and brainwave entrainment are beyond our usual set of experiences, then the evidence that they are having some sort of effect on us must also be outside of our normal range of experiences.

Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry[citation needed] into whether or not the synchronous electrical activity of cortical neural ensembles might not only alter in response to external acoustic or optical stimuli but also entrain or synchronize their frequency to that of a specific stimulus.[16][17][18][19]