Qo'legh is a type of chemical explosive of Klingon origin. It is created by combining three otherwise inert substances, making it a popular tool of covert agents.
Qo'legh was the cause of an explosion aboard Starbase 49 in the year 2287, intended to distrupt a Federation-Klingon peace summit. (TOS novel: In the Name of Honor)
Mackenzie Calhoun used a Qo'legh explosive during his secretive mission aboard the IRW Terix in 2370. (NF - No Limits short story: "Loose Ends")