Trilithium resin was a highly toxic waste product that was produced by the engines of Starfleet vessels in the 24th century. A volatile substance, trilithium resin was sought after for use as a powerful explosive. Storing and moving it was a very delicate process and required specialized equipment.
In 2369, a group of weapons dealers led by Kelsey attempted to steal trilithium resin from the warp core of the USS Enterprise-D while it was undergoing a baryon sweep at Arkaria Base. They were stopped by Captain Jean-Luc Picard (TNG: "Starship Mine").
When introduced into an atmosphere, trilithium resin acted as a biogenic weapon and was lethal to Humans (but not Cardassians). Four hundred kilograms of trilithium resin was enough to make a planet uninhabitable to Humans for fifty years. Captain Benjamin Sisko poisoned the atmosphere of Solosos III with trilithium resin in 2373 in response to Michael Eddington's use of cobalt diselenide (DS9: "For the Uniform").