If a sociologist conceals the fact that they are doing research, they are doing 'covert' research. If they tell group members who they are and why they are there, the research is 'overt'.
Covert research goes against the principle of informed consent and so may be considered unethical. A researcher might argue, however, that the research would be impossible if the group members knew they were being studied, for example if they are involved in criminal activity.
