Europop is a form of music that became popular in Europe1 during the 1970s, and dominated throughout the 1980s. It is typically (but not always) upbeat, synth-driven, slickly-produced, and most of all, catchy. Although it may incorporate some elements in common with its country of origin, Europop is recognisable as such wherever it comes from. Lyrically, it can tend towards the simplistic (thus ensuring its popularity in as wide a range of countries as possible).
ABBA are probably the most successful example of a Europop band (although for all the uptempo, catchy songs they did, it is easy to forget that they had a depth of style and genuine melancholy lacking in many Europop acts). You can find a list of Europop bands at the foot of this article.
Generally speaking, this style of music was never popular in the United States, although some inroads were made by Europop and Euro-influenced acts during the late 1990s2.
Europop is hard to define precisely. Some people would seek to exclude UK-produced music from 'Europop', ignoring the fact that it was the template for most British pop during the 1980s (and, to some extent, the 1990s). Ignore the language, and many J-Pop songs are very Europop in style as well.
Similarly, drawing a line between Europop and Eurodisco- or indeed, Eurodisco and Hi-NRG- is probably counter-productive; they all contain elements of each other. Europop is, like any form of pop, malleable and opportunistic, and doesn't really lend itself to exact categorisation; but it does have a distinct 'know it when you hear it' style.
Europop is also the name of the debut album by French band, Eiffel 65.
1The UK did not really consider itself part of 'Europe' during the 1970s; this is less true nowadays, and many British acts (particularly during the 1980s) are, to all intents and purposes, Europop.
2Aqua's "Barbie Girl" is Europop. I was pretty surprised when I found out that this had been a hit in the US. Ditto Britney Spears' "Baby One More Time", which despite her all-American image is more Europop than the R n'B sound dominant at the time; see 'Max Martin' for more details.
Bibliography and Further Listening