Roshna is a blue liquid substance that has been used by the Goa'uld to keep the race of Aris Boch's home planet subservient as slaves. When it was discovered that Aris Boch's race could not carry symbiotes as hosts, the Goa'uld added the substance to the water supply, and the population became dependent. Without it they would die. Aris Boch trades as a bounty hunter to obtain the roshna he needs to live. He gave Carter a sample of the substance to bring back to the SGC for analysis.
Cross Reference: Aris Boch
Episode Reference: Deadman Switch