Nikon D780 DSLR Camera (Body Only) - Manual (Page 869)

823 Technical Notes
The Low-Pass Filter
Dirt or dust entering the camera when lenses are exchanged or
the body cap is removed may adhere to the low-pass filter and
affect your photographs. The “clean image sensor” option
vibrates the filter to remove dust.
The filter can be cleaned at any time from the menus, or
cleaning can be performed automatically when the camera is
turned on or off.