Is there only one Abyss, viewed both as a place and as a deity?
There is a huge, dark chasm, opening below the Rift. If you ever dare to delve into that darkness, you will certainly notice something. You will... feel the presence of something much older and much more powerful than anything you witnessed before.
There is no such place as Abyss - all you can see and feel there is just a multi-dimensional void, a gaping wound of the universe, inflicted during the Fall.
The Abyss is the energy opposed to the Vortex.
It is static, while the Corruption warps and destroys everything.