Everyone's familiar with disco, of course. Disco was a big hit in the 70s, and a bit into the 80s throughout most of western culture. However, in the US and to a slightly lesser extent in the UK, there was a major backlash against disco, and it came to be viewed very negatively by about 1980 or so, including Bee Gees record burning sessions, and all kinds of other promotional events, including the infamous "day that disco died" when nearly a hundred thousand disco anti-fans showed up at "Disco Demolition Night" in Chicago.
Of course, disco didn't die in much of Europe; in fact, it continued to evolve into numerous forms. Importantly, it lost much of its funk patina, and became a much more recognizably European, dance music form of music. Although I used to take umbrage, during my pretentious younger years, at hearing music critics of the time refer to songs by Depeche Mode or Yaz as "disco" songs, quite frankly, that's pretty much what they were. Disco evolved into electronic dance music, gradually.
As part of this evolution of disco into more modern forms of music, such as Eurodance, came the sideline called italo disco. Italo disco wasn't necessarily all that different from other forms of disco in the early 80s, and its genesis was specifically rather prosaic and even banal rather than artistic. Specifically, the exchange rate between the US dollar and the Italian lira made importing of American music very expensive, and sales plummeted, even though demand remained strong for new music. Local record companies met this demand by having local DJs, producers and other not-quite musicians whip up quick and dirty dance tracks. Many of these artists were disposable (Den Harrow was actually a model who lipped synced in videos, while three different vocalists actually sang and many artists produced a remarkable variety of tracks under several names.) In fact, italo disco became, in a sense, like punk for electronic music--the first "garage band" type of electronic music that was made quick, cheap, and by anyone with a drum machine and a synthesizer.
The vocals were treated more like a another instrument--lyrics were usually in English, but the grammar was often atrocious, the lyrics frequently nonsensical, and they were sung in such a strong accent that you couldn't be sure what they were saying anyway. This quick and dirty Italian music, made primarily in the north (curiously, it was often difficult to find in southern Italy) was originally referred to as spaghetti dance, but when German music label ZYX started importing the music as compilations, they coined the term italo disco, and popularized it throughout central and eastern Europe, as well as much of the Spanish speaking world.
Shortly after ZYX starting bringing it to the rest of Europe, "italo" disco started being made by plenty of non-Italians--Sandy Marton was a Croatian, Fancy was German, Desireless was French, Bad Boys Blue were multinational (but mostly British) who formed in Germany, Sandra was German (with a French mother, and she lived on the French border--and relocated to Ibiza anyway), Baltimora was mostly Italian, but had an Irish frontman, and Taffy and Laura Branigan were American. For instance. Arguably, some of them aren't really italo disco, but on the other hand, how can you really tell? I've never seen that anyone's been rigorous about insisting that their italo disco artists all be Italians. Although curiously, if you don't, then you also run into other problems, i.e., how do you distinguish italo disco from some early Hi-NRG stuff, and other genres that sounded exactly like it? Other than arguably better lyrics (and certainly better pronunciation of them) how is the majority of the Bobby O output really different than italo disco, for instance? Laura Branigan isn't often thought of as an italo disco artist, but c'mon--she mostly sang songs that italo disco artists had written; in fact, her hit single "Self Control" was out literally at the same time as genuine italo disco artist (and songwriter) Raf's version of it was also in the charts--although her version "won" the chart wars everywhere except in Italy. Stuff like Koto could as easily be called space disco (another somewhat obscure genre that actually predated italo disco by a few years) as italo disco, and what do you call stuff like Trans X who actually were native English speakers from Canada? Although not really considered italo disco proper, that kind of music is also strongly associated with it, and most of the internet radio stations I've seen that play italo disco also play Hi-NRG (as per their mandate) and several other closely related and sonically kind of indistinguishable other genres without bias. So clearly the exact boundaries of the subgenre are a bit vague.
For me, I consider italo disco to largely be made up of the guys--and their closely related label-mates and whatnot--that I first heard on the Gapul releases in Argentina. Gapul was also a mixer, and much of what he (she? they?) did was "megamixing"--longish songs made up of portions of italo disco (and occasionally Hi-NRG) tracks. Apparently, italo disco enjoyed some mainstream success in Argentina and Brazil and elsewhere in the Latin world, although by the time I heard it there, it was already kind of old news. I picked up a few megamix compilations that had blatantly obviously gratuitously scantily clad women on the covers and often mangled song and artist crediting, which only made my tracking down of the actual songs a bit more difficult to do. But at the same time, it gave me a strong corpus of songs, at least snippets of which I had heard, that I could track down, and then spread out from there.
Here's Side A of "Lo Mejor de Gapul II"--"The Best of Gapul II." If you like, I can identify any of the tracks on this megamix properly--although I was only ever marginally interested in "Spaghetti" and I never liked anything Spagna did at all.