A mole refers to a person who obtains certain rights or information within an organization, betrays the organization, divulges secrets or engages in other illegal activities. Undercover refers to a secret agent who is infiltrated into criminal gangs or hostile organizations by police, agents and other organizations to obtain information, collect evidence or perform other tasks.

The mole may be a member of the organization or a recruited person. The behavior of the mole is usually out of self-interest or controlled by external forces. Undercover is usually selected and trained, with certain skills and professional knowledge, and their identity and real purpose are kept secret. Undercover's actions are usually to protect social security and fight crime.