'Research chemical' is a term used to describe a psychoactive substance that is mostly untested and new and have had fairly limited use. While originally most of them were psychedelics, there are now stimulants, benzodiazpines, dissociatives, opiods, entactogens, and cannabinoids. Most of these chemicals are legal, although it is possible that the analogue drug laws could apply to many of them. They should not be abused, since long-term effects of these drugs are completely unknown. Careless use of these chemicals can result in hospitalization, and even death, especially when combined with other drugs. Be careful!
Here is a list of the most common research chemicals (if any are missing please /msg me):