Quick Definition: All phenomena are the results of the interactions of matter
Materialism is a form of philosophical monism which holds that matter is the fundamental substance in nature, and that all phenomena, including mental phenomena and consciousness, are the result of material interactions.
Materialism is closely related to physicalism; the view that all that exists is ultimately physical. Philosophical physicalism has evolved from materialism with the discoveries of the physical sciences to incorporate far more sophisticated notions of physicality than mere ordinary matter, such as: spacetime, physical energies and forces, dark matter, and so on. Thus the term “physicalism” is preferable over “materialism”, while others use the terms as if they are synonymous.