The Hirose BM23PF0.8-40DS-0.35V(895) is a 40-position receptacle with center strip contacts from the BM23 series, designed for board-to-board mezzanine stacking. The 0.014" (0.35mm) pitch and 0.031" (0.80mm) mated stack height place it in the ultra-fine-pitch class for compact handheld and portable electronics — think smartphone mainboards, wearable displays, or camera modules where every tenth of a millimeter of z-height is budgeted.
That 0.80mm gap is the clearance between the two PCBs after mating — tight enough for a slim phone or tablet, but it means the opposing connector on the other board must match that exact height. The surface-mount termination with solder retention features keeps the part from shifting during reflow, which matters when you're placing a 40-position, 0.35mm-pitch part and the alignment tolerance is measured in microns.