If a main genre is rock,pop,hip-hop, then emo is a sub-genre of rock, dance of pop, and rap of hip-hop.
Basically, a sub-genre contains elements of another genre, but can't be called that genre. It however, isn't a genre in its own right.
a) Emo is a whole new genre!!
b)Nay, it is but a subgenre
b)Read this! *directs to this article*
a more specific generalization of similar types of art or style (most commonly music) within a less specific genre. subgenres are very constantly changing, as since they are so specific, if a musical artist classified under one subgenre changes their style a little, it may either redefine the subgenre completely or cause the band to be classified under a different subgenre. this may cause confusion, and people tend to be very adamant about knowing what each subgenre stands for, although this representation varies heavily from person to person. subgenres are also commonly misused by shallow dicks to classify people based on their general types of art, style or music.
some MODERN subgenres of the "rock" music genre:more...
grunge -- commonly used to describe a type of rock that's somewhat on the heavy side. throaty voices and guitars with heavy gain and bass are common.
metal -- the heaviest form of rock. the music is sometimes classified as angry, often with screaming or growling voices incorporated, as well as drums with double bass, heavy guitar progressions in a minor key, high gain lead guitar solos, and a fast tempo. metal even has its own subgenres, such as death metal (commonly the music associated with the style generalization of "goths"), hair metal, melodic metal, etc.
punk -- debatably the fastest paced form of rock. often the music is simple, consisting of power chords and simple lead guitar parts very frequently in a major key, and simple but fast paced drumbeats with a fill added every so often. punk is sometimes otherwise defined by politically critical lyrics. this is one of the genres used also to classify a certain group of people, who are often automatically judged as immature, skaters, stoners, and pricks.
hardcore -- music that is similar to metal in its heavy components (such as incorporated screaming vocals, drums with double bass, etc.) but with thinner singing voices, a higher pitched and thinner scream, and a rhythm guitar distortion with less gain and bass and more treble. also a term misused to generalize people as tough or fearless, and usually a style with a lot of body piercings is included in...