What is "downside up"

Downside Up is a four-disc box set collecting B-sides and bonus material from the catalogue of Siouxsie and the Banshees. Also included (on disc four) is The Thorn (EP), originally released in 1984. Most of these songs (only present on these CDs) were classics of the band's live repertoire like "Pulled To Bits", "Eve White/Eve Black", "Red Over White", "I Promise", "Something Blue" and "B-side Ourselves". The boxset was also released on iTunes.