The holographic principle says that all of the information required to represent a 3-D volume is encoded on the 2-D surface of its boundary i.e. in one sense there is no difference between e.g. a black hole and its surface.
The idea is that our universe has three spatial dimensions, but only two are needed to represent a given volume of space. All the information is on the boundary surface.
https://en.wikipedia.org/wiki/Holographic_principle