To go "
undercover" is to avoid detection by the entity one is observing, and especially to
disguise one's own identity or use an assumed identity for the purposes of gaining the trust of an individual or organization to learn or confirm confidential information or to gain the trust of targeted individuals in order to gather information or evidence. Traditionally, it is a technique employed by
law enforcement agencies or
private investigators, and a person who works in such a role is commonly referred to as an
undercover agent.