A bridge camera is a type of camera that fills the niche between relatively simple point-and-shoot cameras and interchangeable-lens cameras such as mirrorless cameras and single-lens reflex cameras (SLRs). They are often comparable in size and weight to the smallest digital SLRs (DSLR), but lack interchangeable lenses, and almost all digital bridge cameras lack an optical viewfinder system. The phrase "bridge camera" has been in use at least since the 1980s, and continues to be used with digital cameras. The term was originally used to refer to film cameras which "bridged the gap" between point-and-shoot cameras and SLRs.