"Dupstep" is actually a typing error made by Lastfm users. The real tag is supposed to be "Dubstep".
During their tagging sprees, listeners did not pay attention as to what they were typing.
Unfortunately, many Lastfm users have made this mistake. Perhaps the confusion may stem from the letter "p" being the reversed shape of the letter "b".
Tag descriptions on Last.fm are editable by everyone. Feel free to contribute!
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