Functionalism (philosophy of mind)
In philosophy of mind, functionalism is the thesis that each and every mental state (for example, the state of having a belief, of having a desire, or of being in pain) is constituted solely by its functional role, which means its causal relation to other mental states, sensory inputs, and behavioral outputs. Functionalism developed largely as an alternative to type physicalism and behaviorism.
Source: Wikipedia — Functionalism (philosophy of mind) (CC BY-SA 4.0)