An awareness spectrum narcotic is any narcotic substance that has the ability to expand an individual's consciousness on some level. This expansion of consciousness could manifest itself in many ways, including prescience, Other Memory, or simply an increase in immediate awareness and sensory ability.
Those who possessed the ability to see into the future when taking awareness spectrum narcotics were considered prescient. Spacing Guild Navigators were capable of such abilities, as were some members of the Atreides genetic line.
Many awareness spectrum narcotics were known to exist throughout the Imperium. The spice melange, which originated on the planet Arrakis, was perhaps the most powerful, and certainly the most widely known throughout the known universe, both during the days of the Imperium and beyond.