A candid photograph is a photograph captured without creating a posed appearance. This is achieved in many ways, for example: when the subject is in motion, by avoiding prior preparation of the subject, ... by not distracting the subject during the process of taking photos.
Candid photography - Wikipedia, the free encyclopedia
Taking photos of people when they have no idea that you’re doing it is called candid photography. One of the beauties of photography is being able to catch someone in the act.