The energy of a physical system can be represented by a mathematical function that depends on several variables. The energy landscape that the system occupies is this function plotted as a hypersurface in space that is one dimension higher than the relevant number of variables. If the energy depends on one variable, then the energy landscape is a line drawn in a two-dimensional plane. If the energy depends on two variables, the energy landscape is a two-dimensional surface embedded in three-dimensional space that can look like mountains and valleys in a real landscape that one might encounter on the Earth's surface. The ground state of a system is the lowest point on the energy landscape.