Which term refers to actions done secretly, especially for purposes of investigation?

The term "undercover" refers to actions conducted in a clandestine manner, typically by law enforcement officers or investigators who operate in disguise or without disclosing their true identity. This approach is often employed to gather intelligence, conduct surveillance, or gather evidence without alerting suspects or the public, thus preserving the integrity of the investigation. Undercover operations are crucial in cases involving organized crime, drug trafficking, and other illicit activities where overt actions would compromise the safety and success of the mission. This term effectively captures the essence of secrecy in investigative procedures.

In contrast, the other terms do not encapsulate this concept of secrecy. "Overt" indicates actions that are open and observable, "obvious" refers to something that is clear or evident, and "public" denotes actions carried out in a way that is accessible to anyone. Each of these terms conveys a sense of transparency and visibility, which stands in stark contrast to the hidden nature of undercover activities.