Hi Lars yeah that is short for "Boundary Representation" it is kind of a more general term than solid, a brep can be a solid or it can be just one more more surfaces that do not form a closed volume.

Basically it means "object made up of one or more surfaces that can be joined along shared edges".

When all edges in the B-Rep are joined to another edge, then that forms a "watertight" skin that encloses a volume - a brep that is set up like that is a solid.

Pretty much all modern solid modeling systems use this method to define a solid volume, but the same structure can hold just one surface, or also joined sheets of more than one surface as well.

It's a somewhat "geeky" term... I try to avoid using it in the program UI but it can be a more natural term to use in a discussion instead of something like "object that may be a surface or more than one surface joined together or a solid..."

- Michael