A form of
danceable instrumental abstract techno music of
Baroque complexity. As the name suggests, it is compatible with
hallucinogens and with losing track of yourself. For the most part it uses a
four on the floor beat at a speed of 130-155
bpm.
Psychedelic trance is is some parts of the world, for instance Byron Bay in Australia or Cape Town in South Africa refered to as psy-trance or simply as trance.
However if you ask for trance in the USA or much of Europe, you are likely to get Paul Oakenfold, Paul van Dyk, or just about any kind of dance music that isn't house. Some of that may be trance, but it definitely isn't psy-trance.
Psychedelic trance is not exactly a synonym for goa. Psy-trance evolved out out of goa trance, and in many cases it is hard to tell on which side of the essentially arbitrary boundary a particular track should fall.
Compare though, the Transcentral 4 compilation mixed by Tsuyoshi Suzuki, which definitely falls on the goa side of the line, and Trancentral 5 mixed by Mark Allen, which is mostly psychedelic trance. Trancentral 6, with hard, driving tracks such as As a child I could walk on the ceiling is definitely not goa.
See particularly Matsuri productions' 1997 release Let it RIP, a psy-trance compilation. The liner notes include the words RIP: Mother Theresa, Princess Diana, William Buroughs, Goa trance. This was news: Matsuri was Tsuyoshi Suzuki's label, so the most respected Goa DJ was declaring it dead along with other high-profile recent mortalities.
As noted in my goa writeup, the psy-trance sound is darker and less uplifting, with a more complex, more European, less melodic and less mystical than goa. Many bands that made goa progressed to making psy-trance. In some respects this represents a loss of innocence and a corresponding gain in experience.
The impetus for the change was the reimportation of the music from the beaches of goa into the clubs of Europe circa 1995, the availability of more sophisticated instruments beyond the TB-303, and the inevitable unending quest for fresh new sounds.
But by 2000 the musical cutting edge had slowly shifted into what is sometimes called psychedelic techno, space techno, or just techno, though some bands still work within the genre of psy-trance. For that matter, some still emulate the goa vibe.