Backpacker:
1. Originally a coined slang term from the 1980s for a graffiti artist that always kept a backpack on containing his finite music collection and more importantly his rattle cans, markers, and spray tips.
Although, mainly his music collection is what defines him/her as a backpacker. Most likely the music collection will consist of usually local underground rap/hip-hop music artists only. The sub-genre or sub-categoration of the music means nothing, as long as they are a local unsigned (no recording contract) artist.
A backpackers music selections are based upon three principals: 1) no mainstream, 2) you could never buy the music in a store, and 3) the music was given/sold to them "hand-to-hand" from the originating recording artist.
2. Modernly used derogatory term to describe someone who listens ONLY to Independent rap/hip-hop music, specifically (but not limited to) the nerd-rap sub-genre of the rap/hip-hop music. Most often used in reference to (but not limited by) white sub-urbanite rap/hip-hop music listeners that tend to dislike mainstream rap/hip-hop music, specifically (but not limited to) Gangsta rap.