Like Goth, Emo is often seen as both a subculture and a sub-genre of rock. Both arose out of the post punk scene, though Emo was more closely an extension of hardcore punk in the US. In its early days it was often describes as "emotional hardcore".
Emo it is one of rock’s many "outsider" sub-genres, having some negative stereotypes associated with it. These often link to emotional angst, introversion and self-harm. Lyrically, songs echo these emotional states; whereas hardcore punk radiated aggression, Emo tends to direct that energy inwards leading, as might be predicted, to unhappiness or even self-loathing.
The 1990s saw bands such as Dashboard Confessional, Weezer and My Chemical Romance gain popularity with some crossover into the mainstream (particularly Weezer).