From Wikipedia: In theoretical physics, a membrane, brane, or p-brane is a spatially extended, mathematical concept that appears in string theory and its relatives (M-theory and brane cosmology). The variable p refers to the spatial dimension of the brane. That is, a 0-brane is a zero-dimensional pointlike particle, a 1-brane is a string, a 2-brane is a "membrane", etc. Every p-brane sweeps out a (p+1)-dimensional world volume as it propagates through spacetime.
From Wikipedia:
In theoretical physics, a membrane, brane, or p-brane is a spatially extended, mathematical concept that appears in string theory and its relatives (M-theory and brane cosmology). The variable p refers to the spatial dimension of the brane. That is, a 0-brane is a zero-dimensional pointlike particle, a 1-brane is a string, a 2-brane is a "membrane", etc. Every p-brane sweeps out a (p+1)-dimensional world volume as it propagates through spacetime.