What does FIDU mean?
In your image, FIDU is the symbol's name for fiducial. Fiducials are used by optical equipment (a pick and place machine) to visually see and locate the board's origin relative to the machine's origin. A small fiducial is probably a 1 mm diameter footprint. Typically, I would place 3 on the top-side of the PCB near the corners and 3 for the bottom-side. I suppose that's why there are 6 shown in your image. Sometimes, additional fiducials are added in close proximity to a large chip/ASIC to help perfectly place (minimize placement tolerances) the chip onto the PCB during PCB assembly.