unfortunately, this field should have been removed in the final version of
the dataset, and is empty for all million songs.
There were discussion about setting it to something meaningful, maybe from
tags, to create a new genre recognition dataset. But this was a bad idea,
later dropped, and the field remained by mistake.
You can always infer a genre (from tags, years, lyrics, ...), but like all
genre recognition sources it would only be a bad proxy.
Columbia University, NY
Ph.D. Candidate, Electrical Engineering