Term variously used.
For Rudolf Carnap (1891-1970), a member of the Vienna circle, it said that all scientific statements could be reduced to statements about ordinary physical objects (or else spatiotemporal points), such sentences having to be publically verifiable. For others it has meant that any meaningful statement can be translated into the language of physics. Currently, physicalism is most often used for the identity theory of mind, sometimes including behaviorism.
All these theories are forms of reductionism.
R Carnap, The Unity of Science (1932); translated with Introduction by M Black (1934)