The view that everything that is real is, in some sense, really physical. See also materialism, knowledge argument, non-reductive physicalism.

In philosophy of mind, the token identity thesis and supervenience thesis are separately insufficient but necessary for capturing the crux of the physicalism.
Pete Mandik

Additional Details:
As used in the philosophy of science, physicalism is the view that all factual knowledge can be formulated as a statement about physical objects and activities. Thus, the language of science can be reduced to third person descriptions.
The positivists defined the physical as that which can be described in the concepts of a language with an intersubjective observation basis. This could be called unity of science physicalism. It is the primary meaning of physicalism in the philosophy of science. Another type of physicalism might be called causal physicalism, the view that all causes are physical causes.
There is a lot of confusion in the phlosophy of mind literature stemming from a tendency to take physicalism and materialism to be interchangeable.
Peter Zachar