Collapse of the universe was a predicted event where the universe stopped expanding and collapsed in on itself, and thus ceased to exist.
According to Jack, our universe will collapse in on itself some time between the next 60 to 70 trillion years. The universe contains too much matter to keep expanding. According to Jack, a massive spherical grid of subspace field generators could be used to manipulate subspace to reduce the mass of the universe and change the cosmological constant. This would avert the collapse. (DS9: "Chrysalis")
Parallel universes could also collapse. A universe inside a warp bubble, shaped by the thoughts of Dr. Crusher in 2367, began shrinking and erasing itself as the warp bubble collapsed. (TNG: "Remember Me") According to Jadzia Dax, it would have been possible to collapse the protouniverse, that was encountered in 2370. The collapse would have been accomplished by suppressing the universe with a force field long enough to allow the feedback pressure to create an implosive wave causing the protouniverse to self-destruct. (DS9: "Playing God")