If rock and pop are the main highway, Indie and Alt are major arterials. The former, short for Independent, was generally a UK term for bands outside the mainstream, often on small non-corporate labels, making music that appealed to select audiences. Both Elvis Costello (Stiff Records) and Aussies The Saints (their first single was self-produced) started here.
The story was similar in the US with ‘Alternative’ artists building passionate followings that sometimes catapulted bands into the big league of commercial success. Nirvana are a fine example, as are The White Stripes.
The Indie/Alt scene is where developments in rock usually emerge; young musicians with a unique vision and fire in the belly. Whether it is punk, prog metal, psychedelia, or any other sub-genre, the grail is to stay true to the original independent vision whilst getting your music heard by the maximum audience.