What is meant by a Domain Walls in cosmology

Originally, all the fundamental forces of nature were unified, but very early in the life of the universe the various forces "condensed" out one by one and became separate in what is called "symmetry-breaking." It's hypothesized that symmetry was broken at slightly different times in different parts (domains) of the universe. Cosmic strings may have formed along the walls that separate domains. I realize that this isn't a very lucid explanation, but it's all that I know about the subject.

"...In cosmology the existence of domain walls, and higher order topological defects such as cosmic strings, monopoles and textures, after a phase transition is assured through the Kibble mechanism. Tom Kibble pointed out that if two regions of space are in causal contact then it is possible for the fields in those two regions to fall into the same vacuum (in the domino analogy they can fall in the same direction). However, if two regions are not causally in contact (they are separated by a distance larger than the distance light could have traveled in the appropriate time) then there is no way to make sure the field falls in the same direction in both places, since they could not have communicated their choices with each other. ..."

http://cosmoaims.wordpress.com/2010/11/1…

This is why I tend to steer clear of cosmology -
http://www.damtp.cam.ac.uk/research/gr/p…
http://cosmoaims.wordpress.com/2010/11/1…