A participant is a person that takes part in a research study. Depending on test object and problem statement appropriate participants for the usability study are selected. Thereby, it is the goal to select potential users that would use the test object in real life. At the same time, it is crucial that participants are unbiased when participating in the research method. They should not be trained or well grounded in the topics of usability and UX, but behave as naturally as they would behave beyond the test situation. That's why for all usability studies, it is essential to observe participants who are real users and behave as natural as possible in order to identify relevant usability problems.