--Hardcore punk (or hardcore) is an intensified version of punk rock usually characterized by short, loud, and often angry songs with exceptionally fast tempos and chord changes.
--Punk rock is an anti-establishment music movement beginning around 1976 (although precursors can be found several years earlier), exemplified and popularised by The Ramones, the Sex Pistols, The Clash and The Damned. The term is also used to describe subsequent music scenes that share key characteristics with those first-generation 'punks'. The term is sometimes also applied to the fashions or the irreverent 'DIY' ('do it yourself') attitude associated with this musical movement.
--Emo (originally short for emocore, itself a contraction of 'emotional hardcore', now usually an abbreviation of 'emotional') is a term now broadly used to describe almost any form of guitar-driven alternative rock that expresses emotions beyond traditional punk's limited emotional palette of alienation and rage. It is also used to describe fans of this genre, most commonly teenagers. (Emo Kid)
--'Screamo' is a music style that developed out of Emo, more specifically hardcore Emo, in the early 1990s. Characteristic of the genre are the screaming vocals (not growling). Other than that, it's fairly hard to classify (particularly since the rule about screaming vocals is bent fairly often). Sometimes also misreferred to as Emo Violence which is a closely related but not identical genre, though each genre borrow ideas from one another. Much like its predecessor, it's very much an underground genre with virtually no mainstream recognition. The majority of screamo bands are from the Northeastern or East coast of the United States (side-by-side with Hardcore coming out of the same area), but there are some bands coming out of Canada, France and Germany, as well as Australia.
big whoop wanna fight about it?