Abstract: Lax, Gel'fand, Oleinik and others have established some fundamental concepts about system of one spatial dimensional conservation laws, such as hyperbolicity, genuine nonlinearity (convexity), linear degenerate, Rankine-Hugoniot condition, stability condition (entropy condition), stability condition(E) and so on. We extend these concepts to system of two spatial dimension case in this note It is a necessary preliminary for advance study.