An informant (also called an informer or, as a slang term, a “snitch”, “rat”, “stool pigeon”, or “stoolie”, among other terms) is a person who provides privileged information, or (usually damaging) information intended to be intimate, concealed, or secret, about a person or organization to an agency, often a government or law enforcement agency. The term is usually used within the law-enforcement world, where informants are officially known as confidential human sources (CHS), or criminal informants (CI). It can also refer pejoratively to someone who supplies information without the consent of the involved parties. The term is commonly used in politics, industry, entertainment, and academia.

In the United States, a confidential informant or "CI" is "any individual who provides useful and credible information to a law enforcement agency regarding felonious criminal activities and from whom the agency expects or intends to obtain additional useful and credible information regarding such activities in the future".