A quantum implosion is a phenomenon which can halt all nuclear fusion within a star, leading to the star's subsequent destruction.
In 2371, Tolian Soran launched a trilithium weapon into the Amargosa star, initiating a quantum implosion. The implosion created a level 12 shock wave which destroyed everything in the system. Soran later attempted to trigger a similar implosion in the Veridian star; he was thwarted by Captains Kirk and Picard.
In an alternate timeline, Soran was successful in destroying the Veridian star and wiping out the inhabitants of the Veridian system. (Star Trek Generations)