A total event collapse was a time explosion which caused the universe to totally collapse, hence the name.
A total event collapse could be caused by a TARDIS exploding, as happened when the Doctor's TARDIS exploded. The Eleventh Doctor seemed to know of them and that the only way to stop a total event collapse was to reboot the Universe. Some things could survive a total event collapse if they were at the centre of the explosion before they were also erased from existence, as happened with the Earth. (DW: The Big Bang)
The Doctor noted that every sun would "supernova at every moment in history" and that "the whole universe will never have existed". (DW: The Pandorica Opens) Though Earth's sun went supernova, Earth itself survived as it was at the "eye of the storm" longer as a meta-temporal event. From the Doctor's viewpoint, the Earth, the moon and the exploding TARDIS existed until 1996, when they too began to fade. Aside from the Moon, the exploding TARDIS, Earth, and it's inhabitants, every star, planet, life form and object was wiped from the face of the Universe, past present and future, across all parallel dimensions. Those races present near the initial explosion, namely, the Alliance, were preserved as stone statues. These species included the Daleks, Cybermen, Judoon, Silurians, Sontarans, Atraxi, Slitheen, Autons, and Nestene.
The Doctor reversed the total event collapse with the Pandorica, which contained some atoms of the former universe, flying it into the heart of the TARDIS and causing the Big Bang Two to reset the universe. (DW: The Big Bang)
A total event collapse could also change some species' histories. A Cyber-Leader noted that "all universes will be deleted", which suggests a total event collapse also affected parallel worlds. (DW: The Pandorica Opens)