Phase space

The phase space of a physical system is the space containing all possible states of the system in a given parameterization. It is the space of canonical coordinates of the system. In mechanical systems, the parameters are typically the position $\mathbf{q}$ and the momentum $\mathbf{p}$ of each particle, but more generally they are the generalized coordinates and conjugate momenta. For a system with $n$ degrees of freedom, the phase space is $2n$ dimensional. Each point in phase space represents one possible state and is called a representative point.

In differential geometry terms, the phase space is the cotangent bundle of the configuration space.