In its strong form, the thesis that there is no knowable reality behind appearances. Thus, it is the job of science to catalog the formal relations which hold between appearances without claims of describing reality. See phenomenalism.

Such forms of empiricism may or may not admit of the existence of a reality which is trans-empirical. The transcendent nature of reality determines that we can have no knowledge of it and thus must simply catalog the formal relations between appearances. Logical empiricists (aka logical positivists) used this position to suggest that all 'metaphysical' claims are meaningless.
Empiricism is very much like phenomenalism. However, empiricism is a term more commonly used in philosophy of science or epistemology than philosophy of mind. In either case, this kind of position is most commonly contrasted with realism.
Chris Eliasmith