Electro is a kind of dance music that uses electronic sounds — drum machines, synthesizers, a hard, often robotic beat. It grew in the late 1970s and 1980s, close to early hip-hop and funk made with machines, and people still use the name for later tracks in that style. DJs and young listeners say electro; it is informal. It is a clipping of electronic, but it is narrower than “electronic music,” which covers a huge family of styles (house, techno, ambient, and more). If you only mean “music made with computers,” say electronic music. Electro points to that particular sound. Though actually, you will also see electro- stuck on the front of other words (electroshock, electromagnetic). That is a prefix meaning “electric,” not this music sense. The entry here is the music. You may hear older people just say “electronic music” for everything; younger club-goers are more likely to keep the short name for this style.