I came across this majestic theory while reading the National Geographic Answer Book on fast facts about the world. It's fascinating and I think you'll find it just as interesting as I did! Let me share a quick explanation.

A brane is a physical object in string theory and other theories that generalizes the idea of a point particle, string, or membrane to higher dimensions. The word "brane" is short for "membranes" - Google

Mathematicians and astrophysicists considering the existence of other uni-verses must entertain the possibility of more dimensions than the four we know as space-time: the three famil-iar dimensions plus the dimension of time, added by Einstein. In one version of string theory, physicists allow for eleven dimensions, including seven that remain imperceptibly "curled up." The visible universe could be a four-dimensional membrane, or brane for short, moving through unseen dimensions. Other branes, or paral-lel universes, may also exist, floating through a fifth dimension that we can-not perceive. Some scientists propose that our would-be universe existed as a brane into which another brane collided in a uniform fashion, generating the heat energy and expansion accounted for in the big bang. But these theories now exist main-ly as mathematical models that require much additional investigation.