Originally Posted by Wikipedia

Emo ( /ˈiːmoʊ/) is a style of rock music characterized by melodic musicianship and expressive, often confessional lyrics. It originated in the mid-1980s hardcore punk movement of Washington, D.C., where it was known as "emotional hardcore" or "emocore" and pioneered by bands such as Rites of Spring and Embrace. As the style was echoed by contemporary American punk rock bands, its sound and meaning shifted and changed, blending with pop punk and indie rock and encapsulated in the early 1990s by groups such as Jawbreaker and Sunny Day Real Estate. By the mid 1990s numerous emo acts emerged from the Midwestern and Central United States, and several independent record labels began to specialize in the style.

Originally Posted by RYM

Since its origination in the mid-80s, Emo has undergone many changes both stylistically and in the public perception of what exactly the term means. To attempt to nail down a singular standard for all Emo here would be folly, as no such thing exists. The unifying factor that makes emo (short for emotional) what it is, is a determination to use deeply personal and sincerely expressed feelings the central theme, whether that be through furious anger and personal climax or by heartfelt confession and poetic crooning.

There is general agreement that the origins of Emo grew out of the Washington, D.C. area Hardcore Punk scene, as former punk rockers looked for new forms of expression and formed the bands Rites of Spring and Embrace. The scene quickly spread to California, then across the landscape. The early Emo scene (1984-1989) sound featured mid-tempo, rock based guitar with an occassional flourish riff, and punk vocals that were sung rather than yelled. Emo was at this point still largely underground.

A second wave of emo bands like Moss Icon emerged around the turn of the decade, and introduced new elements to the sound. The quiet/loud dynamic became popular, as well as catchy riff based songs featuring octave chords, pop song structure, and more mainstream, clean vocals. It could be argued that the genre's first breakout band was Sunny Day Real Estate, and this style of Emo is what has stuck in many people's heads as definitive of the style, although during this same period bands like Mohinder were playing a more abrasive, punkish Emo featuring staccato, distortion-wracked music over screamed vocals. A divergence was already apparent.

From the mid-90s onward, this style of indie/post-rock-leaning Emo remained the larger sect, and spawned armies of like-minded bands. Though far removed from its roots, this incarnation has expanded the Emo fanbase into a major demographic as groups like The Get Up Kids and Dashboard Confessional carry the style toward the pop commercialism that its originators detested.