In psychological research studies deception refers to misleading or tricking participants about the purpose or direction of the study. This is an important component of research in that if participants know what the experiment is about then the results can possibly be influenced such as when participant bias occurs.
For example, experimenters are interested in the food choices of individuals in unfamiliar social situations. They place a wide variety of snack foods on a table in the room where the participants show up for the experiment.
The experimenters could then tell the participants that they were going to complete a written memory test but to help themselves to snacks while the test room was being set up. The participants choose their food while the experimenters are watching and recording their choices. This is a classic use of deception - the participants think they are waiting to complete the real experiment when in fact they are unknowingly giving the experimenters the information they are really interested in.