Apparatus broadly refers to the equipment, machinery, or structure that is necessary for a particular purpose or activity.
In psychology, this means the equipment or measures that are necessary for conducting research.
Apparatus can refer to any equipment used in an experiment such as cages, machines, computers, heart rate monitors, or brain imaging machines. Typically any equipment or tools used in a study are listed in the methods section of a research paper under the subheading "Apparatus and Materials." An alternate usage can refer to a human organization such as a political structure referring to the people and procedures that are necessary to run an organization. In biology, apparatus can refer to a system of structures that perform a particular function together, for example the Golgi apparatus.