What is "spice" found in smoke shops? I know it is a synthesized cannabinoid, but that's it.

Synthetic Cannibis. "spice" is the generic name for synthetic cannibis. Originally marketed as a legal alternative to marijuana testing has since shown that they contain synthetic cannabinoids. They produce a high like marijuana though more psychogenic. The dea and most states made these products illegal. These drugs may induce a more psychogenic experience than marijuana with a higher risk of physical addiction.
Can be bad stuff. And that it is wayyyyyy more dangerous than natural cannabis, which can itself cause problems in some people. Spice and k2 have much more variability in dose, even between puffs of the same stuff, and sometimes people hit hot-spots with very high dose, and psychosis, hallucinations, delirium and even death have been reported, especially but not only in naive users. Stay away from it!