Not a mood or a lifestyle — a specific claim about what the universe is made of.
In everyday use, “materialism” usually means valuing possessions too much — a moral complaint about consumer habits. Philosophically, it means something much more specific and much older: a thesis about the fundamental nature of reality itself, not a judgment about anyone’s spending.
As a metaphysical thesis, materialism holds that the actual world conforms to the condition of being physical — and that anything which doesn’t look physical at first glance (a thought, a value, an institution) is nonetheless physical, or at least fully dependent on the physical, once properly understood. The word entered English toward the end of the 17th century; “physicalism,” the term philosophers now often use interchangeably with it, wasn’t coined until the 1930s.
A framework built on this premise has, by definition, no room for anything — revelation, an immaterial soul, a moral order independent of physical utility — that doesn’t ultimately reduce to matter and its interactions. That’s the stronger, structural sense at stake whenever a critique of “materialism” is doing more than complaining about consumerism. Source: Stanford Encyclopedia of Philosophy, “Physicalism” entry.