Progressive House, also known as Trance House or Trancehouse, is a modern subgenre of the House genre of music. As you may or may not remember, House is a genre that is for the most part known for being based on a 4:4 time signature, being electronically produced, as well as being an offshoot of disco. More importantly, however, House was the first type of music to be directly associated with DJ's and the DJ subculture, and remains so to this day, mainly for its ease of mixing, catchiness, and crowd control value (it is very easy to dance to, and it really tends to take control of one's body). To this day, the majority of good House only comes out on vinyl, and 99% of the House that comes out on CD's comes out on vinyl way before it gets out on CD. To put it bluntly, Progressive House is a more DJ-friendly version of Trance. Where Trance can be tricky to mix because of changes in BPM, sudden transitions, etc, Progressive House has a similar sound to trance, but it is a lot easier to mix because of the lack of the tricky stuff.
What identifies Progressive House?
What separates Progressive House from the other genres of House music, is that instead of just giving you the dancey party feel of Disco House or Deep House, etc, it gives more of the trancey feel of flying, but slowed down a bit. Prog House, as a matter of fact, instead of using real instruments, is much closer to Techno, utilizing almost exclusively synthesizers. It also typically has a lower probability of having vocals.
What artists have been involved in the creation of Progressive House?
Progressive House is fairly new in the world of electronic music as compared to its cousins, Deep House, Filtered/Disco House, et al. Some artists that have lately made it popular are BT, and to a lesser extent, Sasha, Paul Oakenfold, and Deep Dish and the other well-known House artists.
What are the more specific characteristics of Progressive House?
One of most reliable signs that a song is Prog House, and the most unique characteristic of most of the songs in the genre is the simplicity of their melodies. Be prepared, as with most House, to hear only one melody, and with Prog House, it is generally made to be the part of the music that you notice, more so than the other subgenres. The melody will usually be extremely catchy, which is one of the things that makes Prog House so addictive. Despite this simplicity, however, Progressive House sits right up there with all the other Dance music in being very danceable, and being a crowd favorite. (On a side note, Prog House sometimes gets so close to Dance music that it's near impossible to definitely distinguish which it is.) So the question you might be asking is, "Why is Prog House so successful even though it is so simple, sometimes to the point of being amateurish?" Well, here is the reason.
In Progressive House production, less attention is paid to the melody, and much, much, much more to the actual instruments, namely the synthesizers. Most of the more exotic synths around will be found not in Trance, but in Prog House, and to a lesser degree, Dance. Expect to hear really nice sounding synths, with lots of layered effects that make it sound all the more unique. (Another side note: BT's style of composition is taking apart the music to an almost genetic level, tweaking every note, and paying extreme attention to detail, especially in instruments. Think of Prog House production, and then think of BT's production style, and there you have why BT is one of the pioneers of Progressive House.)
In short, Prog House is the opposite of traditional music, and in doing so, does a damn good job of being danceable, mixable, and having great crowd control characteristics.
IMPORTANT NOTE: Prog House is NOT to be confused with plain old Trance music. They have a lot of parallels, but are different genres. There are, however, many opinions on what is a subgenre of what, but it is generally understood that the two are different things.
Sources: Listening to a fuckload of House and Progressive House, both individually and as part of live sets.