A candid photograph is a photograph captured without creating a posed appearance. The candid nature of a photograph is unrelated to the subject’s knowledge about or consent to the fact that photographs are being taken, and unrelated to the subject’s permission for further usage and distribution.
Taking photos of people when they have no idea that you’re doing it is considered candid photography. One of the beauties of photography is being able to catch someone in the act. It adds life to your pictures.