Definitions for "Occasionalism"
The system of occasional causes; -- a name given to certain theories of the Cartesian school of philosophers, as to the intervention of the First Cause, by which they account for the apparent reciprocal action of the soul and the body.
Malebranches' idea on how the mind and body could interact - namely, that naturally they didn't, and God had to intervene to allow the soul to affect the physical world each and every time you do something. Now justly considered ludicrous.
The theory that mind and body are separate realities which do not interact but that events occur in one as they occur in the other according as God wills their occurrence. (Malebranche)