Spice was slang for a mind-altering drug. Varieties included ryll, andris, lumni, avabush, carsunum, and the strongest (and most expensive), glitterstim. Planets such as Kessel, Ryloth, and Sevarcos were rich with these spices, which were harvested from dangerous mines. More often than not, harvesting was done by slave labor.
The Galactic Empire attempted to keep a tight rein on the circulation of the various forms of spice, making it a frequent item for smuggling. It must be noted though, that not every form of spice was addictive, or even illegal.
In 194 BBY, the term "spice" gained widespread use.1