Electro (short for either electro-funk or electro-boogie) is a genre of electronic dance music directly influenced by the use of TR-808 drum machines, and funk sampling. Records in the genre typically feature drum machines and heavy electronic sounds, usually without vocals, although if vocals are present they are delivered in a deadpan manner, often through electronic distortion such as vocoding. This is the main distinction of electro from previously prominent genres such as disco, in which electronic sound was only part of the instrumentation rather than basis of the whole song.
Definition and characteristics
From its origins, the definition of the electro sound is the use of drum machines as the rhythmic base of a track; however as the style has evolved, and with the advent of computer usage in electronic music, the use of drum machines has become less and less practical and widespread. Electro drum patterns tend to be electronic emulations of breakbeats, with a syncopated kick drum, and usually a snare or clap accenting the downbeat. The difference between electro drumbeats and breakbeats (or breaks) is that electro tends to be more mechanical, while breakbeats tend to have more of a human-like feel, like that of a live drummer. The definition however is somewhat ambiguous in nature due to the various use of the term.
Staccato, percussive drumbeats tend to dominate electro; with beats once mostly provided by the Roland TR-808 drum machine, the advent of computers in electronic music has outdated this old school method and are now used by the majority of electro producers the world over. The TR-808, created in 1980, has an immediately recognizable sound, and through the use of samples remains somewhat popular in electro and other genres to the present day. Other electro instrumentation is generally all-electronic, favoring analog synthesis, bass lines, sequenced or arpeggiated synthetic riffs, and atonal sound effects all created with synthesizers. Heavy use of effects such as reverbs, delays, chorus or phasers along with eerie synthetic ensemble strings or pad sounds emphasize the common science fiction or futuristic theme of the lyrics and/or music. “Light Years Away” (1982) by the electro group Warp 9, a “sci-fi tale of alien visitation” written and produced by Lotti Golden and Richard Scher, exemplifies this style of electro.
Most electro is instrumental, but a common element is vocals processed through a vocoder. Additionally, speech synthesis may be used to create robotic or mechanical lyrical content, as in the chorus of "Nunk" by Warp 9.  Some earlier electro features rapping, but that lyrical style has become less popular in the genre from the 1990s onward.
About electro-funk origins, Greg Wilson claims:
"It was all about stretching the boundaries that had begun to stifle black music, and its influences lay not only with German technopop wizards Kraftwerk, the acknowledged forefathers of pure electro, plus British futurist acts like the Human League and Gary Numan, but also with a number of pioneering black musicians. Major artists like Miles Davis, Sly Stone, Herbie Hancock, Stevie Wonder, legendary producer Norman Whitfield and, of course, George Clinton and his P Funk brigade, would all play their part in shaping this new sound via their innovative use of electronic instruments during the 70’s (and as early as the late 60’s in Miles Davis’s case)."
Following the decline of disco music in the late 1970s, various funk artists such as Zapp & Roger began experimenting with talk boxes and the use of heavier, more distinctive beats. Electro eventually emerged as a fusion of different styles, including funk and disco combined with German and Japanese electropop, in addition to influences from the futurism of Alvin Toffler, martial arts films, and video game music. The genre's immediate forebearers included Kraftwerk, Yellow Magic Orchestra (YMO), and Gary Numan. An important precursor to the genre was Cat Stevens' "Was Dog a Doughnut" in 1977.
In 1980, YMO was the first band to utilize the TR-808 programmable drum machine. That same year, YMO member Ryuichi Sakamoto released "Riot in Lagos", which is regarded as an early example of electro music, and is credited for having anticipated the beats and sounds of electro. The song's influence can be seen in the work of later pioneering electro artists such as Afrika Bambaataa and Mantronix.
In 1982, Bronx based producer Afrika Bambaataa released the seminal track "Planet Rock", which contained elements of Kraftwerk's "Trans-Europe Express" (from the album of the same name) and "Numbers" (from Kraftwerk's 1981 Computer World album), as well as Yellow Magic Orchestra songs such as "Riot in Lagos" (from Sakamoto's 1980 album B-2 Unit). "Planet Rock" is widely regarded as a turning point in the electro genre. That same year, although remaining unreleased, a pre-Def Jam Russell Simmons produced Bruce Haack's proto hip-hop single "Party Machine" at a studio in Philadelphia. "Nunk," by Warp 9 also released in 1982, exemplified "imagery drawn from computer games, video, cartoons, sci-fi and hip hop slanguage."
In 1983, Hashim created the influential electro funk tune "Al-Naafiysh (The Soul)" which became Cutting Record's first release in November 1983. At the time Hashim was influenced by Man Parrish's "Hip Hop, Be Bop", Thomas Dolby's "She Blinded Me With Science" and Afrika Bambaataa's "Planet Rock". "Al-Nafyish" was later included in Playgroup's compilation album Kings of Electro (2007), alongside other electro classics such as Sakamoto's "Riot in Lagos". Also in 1983, Herbie Hancock, in collaboration with Grand Mixer D.ST, released the hit single "Rockit".
Bambaataa and groups like Planet Patrol, Jonzun Crew, Mantronix, Newcleus and Juan Atkins' Detroit-based group Cybotron went on to influence the genres of Detroit techno, ghettotech, breakbeat, drum and bass and electroclash. Early producers in the electro genre (notably Arthur Baker, John Robie and Shep Pettibone) featured prominently in the Latin Freestyle (or simply "Freestyle") movement. Detroit techno DJ Eddie Fowlkes shaped a style called electro-soul, which was characterized by a predominant bass line and a chopped up electro breakbeat contrasted with soulful male vocals. Kurtis Mantronik's electro-soul productions for Joyce Sims presaged new jack swing's combination of hip hop and soul elements.
By the late 1980s, the genre had parted from its initial funk influences. Baker and Pettibone enjoyed robust careers well into the house era, and both eluded the "genre trap" to successfully produce mainstream artists.
...more info at http://en.wikipedia.org/wiki/Electro_%28music%29