For a system of n first-order ordinary differential equations (or more generally, Pfaffian forms), the 2n-dimensional space consisting of the possible values of (x_1, x^._1, x_2, x^._2, ..., x_n, x^._n) is known as its phase space. If n = 1, the phase space is known as a phase plane.

phase | phase flow | phase plane | phase portrait | world line