A subgenre of electronica which combines steady, mono-temporal beats with more atmospheric, layered sounds such as pads, strings, repetitive vocal or percussion sounds, and experimental noises. Generally, an entire trance song is based around a single chord, but with quite a bit of melodic variation around the theme. The general goal of trance music is, as the name suggests, to put the listener into a trance-like, consciousness altered state. Much trance music is suitable not only for dancing to, but also for non-dancing critical listening; this somewhat sets it apart from most other electronica subgenres. (See IDM.) In fact, many trance enthusiasts find that listening to the music is quite relaxing, despite the steady beat.
Trance also employs dynamics to a greater extent than most other forms of electronica. A characteristic of many trance songs is the mid-song break in which the rhythm tracks are faded out, leaving the melody and/or atmospherics to stand alone for a few moments. If one counts out the bars during this time, it will usually be found that the track is still on tempo, but it isn't obvious since there is no instrument carrying the beat at this point (a trick enabled by sequencers). The break adds some dynamics to the song, makes it more interesting to the ear, and provides dancers with a few moments in which they can improvise if they wish. Other trance songs may fade in to begin the song, or end the song with atmospherics or odd noises rathenr than the usual rhythm "tail". Fashion tends to go back and forth between vocal and instrumental pieces every few years; usually when vocals are present, they are sung by a female singer with a soaring, operatic type voice.
Trance's origins are rather murky. Some sources have it originating in Germany around 1993, others place its beginnings in Great Britian. DJ George Acosta, who studies the history of trance, compiled a CD of essential early trance records on which he placed Brian Transau's "Anomaly Calling Your Name", released in 1995, as the first song. The genre enjoyed a boom in popularity right away, dominating the electronica scene in the late '90s before fading away somewhat at the millenium. However, a resurgence has taken place since about 2005.
Goa trance is an offshoot of the form, originating in Goa, India, where a sort of continuation of 1960s San Francisco psychedelic culture existed in the 1990s. As one might expect from that description, Goa trance employs elements of '60s psychedelic and "swirl" music.