The cosmos (UK /ˈkɒzmɒs/, US /ˈkɒzmoʊs/) is the universe regarded as a complex and orderly system; the opposite of chaos. The philosopher Pythagoras used the term cosmos (Ancient Greek: κόσμος) for the order of the universe, but the term was not part of modern language until the 19th century geographer and polymath, Alexander von Humboldt, resurrected the use of the word from the ancient Greek, assigned it to his multi-volume treatise, Kosmos, which influenced modern and somewhat holistic perception of the universe as one interacting entity.
Cosmology is the study of the cosmos in several of the above meanings, depending on context. All cosmologies have in common an attempt to understand the implicit order within the whole of being. In this way, most religions and philosophical systems have a cosmology.
Cosmology is a branch of metaphysics that deals with the nature of the universe, a theory or doctrine describing the natural order of the universe. The basic definition of Cosmology is the science of the origin and development of the universe. In modern astronomy the Big Bang theory is the dominant postulation.