During the "first wave" of electronic dance music in the US (mid-late 90s into early 00s), stuff like Prodigy, Moby, Underworld, Crystal Method, Chemical Brothers, etc. were called "electronica" or "techno" (adding to massive confusion for people who understood techno to be its own genre in the same way that "metal" would be considered a separate/subgenre of "rock").
EDMC ("electronic dance music culture") was used as early as 2006 in academia to describe a wide range of cultures stemming from rave, free party, and club culture.
However, in the early 2010s, the EDM term began to be used by large companies to better market electronic dance music, which had grown in popularity a great deal in the late 2000s. The most popular forms of electronic dance music were embedded into a lot of commercial marketing tactics, and what this resulted in were people associating certain musical styles with EDM (e.g. dubstep, electro house, big room house) - namely the styles that happened to be popular at the time. The music often featured a song structure that I now english news capread call the "pop EDM song structure" - intro->breakdown->build-up->drop section->breakdown->build-up->drop->outro. Common pop music techniques were embedded into the breakdown sections of these songs, and the music began to focus a great deal on creating epic build-ups and/or highly emotional/euphoric breakdowns. This kind of musical form was already present in trance, but trance never reached the popularity that dubstep/electro house/big room/festival house/trap has reached in the US. You will probably notice that almost all of the music on this sub features the song structure I mentioned previously. It won't necessarily be the case in electronic.