Emo is a style of rock music which describes several independent variations of music with common stylistic roots. Such use of the term has been the subject of much debate. In the mid-1980s, the term emo described a subgenre of hardcore punk which originated in the Washington, DC music scene. In later years, the term emocore, short for "emotional hardcore", was also used to describe the emotional performances of bands in the Washington DC scene and some of the offshoot regional scenes such as Rites of Spring, Embrace, One Last Wish, Beefeater, Gray Matter, Fire Party, and later, Moss Icon. (In more recent years, the term "emotive hardcore" entered the lexicon to describe the period.)
Starting in the mid-1990s, the term emo began to refer to the indie scene that followed the influences of Fugazi, which itself was an offshoot of the first wave of emo. Bands including Sunny Day Real Estate and Texas Is the Reason had a more indie rock style of emo, more melodic and less chaotic. The so-called "indie emo" scene survived until the late 1990s, as many of the bands either disbanded or shifted to mainstream styles. As the remaining indie emo bands entered the mainstream, newer bands began to emulate the mainstream style. As a result, the term "emo" became a vaguely defined identifier rather than a specific genre of music.
Some of the new bands such as Fall Out Boy, Lostprophets, Paramore, My Chemical Romance, The Used and Thirty Seconds To Mars and made a real impact for emo fashion. Either that people or "kids" copying there style or buying clothing ranges run or worn by the band.
Some of the brands that have really made it big in the emo clothing circle are:
FAMOUS STARS AND STRAPS, DROP DEAD, KILL BRAND AND TO DIE FOR
If you think this is not enough info for you why not check out these videos on how to be emo and also on emo clothing.