A synonym for the universe, the cosmos is the entirety of matter and energy. The word cosmos derives from the Greek word kosmos meaning the structure and harmony of the entire world.

The entire physical universe, all matter and energy, comprise the cosmos. Matter is any physical substance that occupies space and has mass. The smallest and most basic units of matter are subatomic particles, like protons, quarks, positrons, neutrinos, and electrons. The identity of a singular unifying subatomic unit that comprises all matter in the cosmos remains elusive. Energy, in contrast, is an ambiguous concept, a function of state, that can most usefully be described as the capacity to do work. Energy exists in many forms, including potential and kinetic energy.

Occasionally, the term cosmos is improperly used to denote the universe apart from Earth. In its truest sense, however, the cosmos includes the Earth as well...