Ambient music has a rhythmic or trance-like nature, with (generally) electronic keyboards and/or spacemusic melodies or themes. Notably, it is the consistent combination of varying elements that provides a common thread or theme throughout ambient music. Today's ambient music, usually referred to as "New Ambient" or "Ambient Dub," means full of rhythms, for dance or trance, body movement or mind relaxation mode, and often sounds floaty or "groovy," with drop-out beats, tribal treats, ethno-primitive, textural and/or cyber-phonic music. Curiously, the previous view or definition of ambient music suggested no rhythm, carving backgrounds that were potentially fertile foregrounds, a la Eno, Budd, Roach, Stearns, Schulze or early Tangerine Dream. Ambient music grew into its own genre out of the "chill-out" rooms that became a part of the rave scene, a place to escape the pounding, throbbing techno beats (often in excess of 160-180 beats per minute!), where DJ's mixed together nature sounds, New Age music tracks, and tape loops or other sound samples. As greater skill emerged in the molding of these sound spaces, CDs were issued which were usually compilations Excursions in Ambience, From Here to Tranquility, United States of Ambience, Ambient Dub, Ambient Extractions, Chill Out, Feed Your Head, One A.D., etc. As we watch the ever-evolving growth and fast-rising emergence, and acceptance, of this genre, we often hear terms like "mutated," or "deconstructed" i.e. anti-categorization at best. It is also of interest to note that many artists (and stores) really prefer the term Ambient to "New Age" thereby confusing the issue even more since they are rarely the same thing, albeit closely related at times. Similar appeal, yes; similar sound only in one sub-genre of Ambient music (read on...)
I see six different types of Ambient music. There is, of course, much crossover, as there is in any style. But I will cast these as currently definitive, and feel that at the very least they act as a good guide for store-owners and consumers alike.
New Age music, while commonly used as a "banner" heading, can still be separated as a specific style, generally void of rhythm, meditative, relaxing, etc. Similarly, Spacemusic is a specific type, as represented by Jonn Serrie, Kevin Braheny, Steve Roach, etc. It conjures up either outer "space" or "inner space", and is heard in Planetariums, on massage tables, and as soundtracks to many videos and movies. As explained above, Ambient music is a broader term, encompassing (at least) six sub-genres, part of which includes New Age or Spacemusic. Also, a new generation of musicians, meaning usually a younger generation, that have come from techno, dance, rock and punk realms rather than a general tracing back to New Age ideas or circles that was prevalent 10-15 years ago and mostly since. While Brian Eno has been (reluctantly) lumped into New Age association, he has much more "fathered" this generation than perhaps anyone else. Part of this is strictly nomenclature, and which term is more appropriate for the overall general section. Most stores in the record industry have a New Age section; some may be tempted to call it Ambient and hence can finally discard the New Age term. But let's not be hasty! The New Age banner fits nicely over the whole section for record stores. But for bookstores and specialty stores it's different. Their categories tend to be more along the lines of tribal, meditative, world, drumming, vocals, Native American, Celtic, shamanic, massage, guitar, piano i.e. by instrument, "usage," or music type, as perhaps all of their titles fit under the broad New Age term. And that leaves room to segment or group the ambient titles, shown above as examples, to tie into certain radio shows, local dance venues, etc.
Several directions simultaneously! And, yes, it is specific... Most of this map has been laid out and clarified over the past 10-12 years. Suppose you were to draw a wheel. Each spoke, tracing a thin pie-shape out of the whole, would contribute to the modern or New Ambient movement: new age, neo-classical, space, electronic, ambient, progressive, jazzy, tribal, world, folk, ensemble, acoustic, meditative, and back to new age... The order and placement is no accident; each comes in and out of the previous, leading into the next, with shades of overlap and crossover visible at every turn. Each "type" has its own history, its own cornerstones and "hall of fame" artists and titles. Each has crystallized and grown, achieving greater artistry over time, and becoming more recognizable in the marketplace. A more far-reaching answer addresses the real challenge, which is dictated by today's machines i.e. synthesizers, and how their use and placement is balanced by human kind's ability to interface with the machines. Man's inherent ability to adjust artistic integrity in keeping with the times demands sensitivity to the roots, the spirit of the music, the calling of past generations and the need for continual originality. More in this hybrid ambient music than perhaps anywhere else is this challenge being met; that is why people are responding so favorably to the combining of elements rhythm'n'space, tribal cultural intermixes that open the mind and move the body.