Deception refers to concealment of the purpose and procedures of a study from the participants.
Other /More definition:
Deception means concealing or camouflaging the real purpose of an experiment from the participants; a research technique in which the participant is misled about some aspect of the project which may be unethical.
Sometimes, Deception is used in research when knowing the true purpose of a study would change the participants' responses or produce non-veridical data.
Lexicon of Psychology - Terms, Treatments, Biographies,