举报人是指声称要揭发行为不检、不实或者非法的人士。这些不良行为可以分为很多种类，如：违反法律、规章、条例或者威胁公众利益，又或如造假、危害公众安全卫生和贪污等。举报可能会在内部提出（譬如说是向组织内部的其他人员）或者向外界诉求（如：立法者、法律机构、媒体或者关注人士）。

第一条有关保护举报人的法律于1778年7月30日通过殖民国会。1777年举报人Richard Marven和Samuel Shaw遭受殖民海军总司令Esek Hpkins的报复事件后，殖民国会便敦促制订此条法律。国会宣布，美国会为这两名举报人所受Esek Hopkins的诽谤诉讼提供辩护。随后国会也宣告，所有为美国效力以及在其国土上生活的居民，均有责任告会国会或者相关部门政府公务官员不检点、造假和不良的行为。

An informant is a person who provides privileged information about a person or organization to an agency. The term is usually used within the law enforcement world, where they are officially known as confidential or criminal informants (CI), and can often refer pejoratively to the supply of information without the consent of the other parties with the intent of malicious, personal or financial gain. However, the term is used in politics, industry and academia.