Electronica is a genre of music most often heard in either nightclubs or in lounges. It's never really made the mainstream like rock-n-roll and hip-hop/rap eventually did. Even as it operates in the fringes, it is now increasingly mainstream - on movie soundtracks, advertisements, as background themes on TV shows, pretty much everywhere.
In an excellent review of the genre and some seminal albums, this writer says:
"Electronic music gets attacked as somehow less "real" than everything else — as if (1) the electricity that powers a guitar differs from the electricity pumped into a synthesizer, (2) hands holding drumsticks are unlike the hands used to trigger a drum-machine and, most crucially, (3) the sounds we hear as listeners owe their allure to the process by which they're made. "