Definition: The braneworld is a contemporary picture of our universe, which speculates that our visible universe may be confined to a three-dimensional volume which resides in a higher-dimensional space. This picture is motivated by superstring theory and M-theory. Brane is short for ‘membrane,’ the fundamental object of a scenario of the high-energy physics of braneworld (or brane cosmology).
More about the term: If it’s proven right then it constitutes a major revision of our understanding of the universe. This would also be similar to Max Tegmark’s level three and four multiverse; however, this would belong in a bit of a different category from Tegmark. This is primarily advocated by Columbia physicist Brian Greene and is known as… Braneworld.
Here’s a relevant paper abstract:
The aim of these lectures is to give a brief introduction to brane cosmology. After introducing some basic geometrical notions, we discuss the cosmology of a brane universe with matter localized on the brane. Then we introduce an intrinsic curvature scalar term in the bulk action, and analyze the cosmology of this induced gravity. Finally we present the cosmology of a moving brane in the background of other branes, and as a particular example, we discuss the cosmological evolution of a test brane moving in a background of a Type-0 string theory.