The trilithium torpedo is a superweapon developed by Dr. Tolian Soran. It uses trilithium -- a biproduct of the Federation's matter-antimatter power system -- to cause the rapid collapse of a star. The collapse also produces a powerful subspace shockwave that is destructive to planets, ships, and other objects in the system. It's not clear whether there are limits on what types of stars can be affected or what is the full extent of the damage inflicted on objects in the system.
The only existing examples of the device were either used or destroyed on the launch pad, and all data on its design was lost with the destruction of the Klingon Bird of Prey on which it was carried.