We present a unified description of spherical discontinuity surfaces in General Relativity based on two parameters: mass function and surface permeability. The surfaces considered are: \textit{ Impulsive fronts}, massive permeable layer; \textit{ Surface layers}, massive impermeable layer; \textit{ Shock fronts}, massless permeable surface; and \textit{ Boundary surfaces}, massless impermeable surface. We derive the exact jump conditions for the physical variables across all these surfaces. Finally, we discuss the quasi-static approximation from studying slow hydrodynamic processes involving discontinuity surfaces.
Categories: gr-qc