The 54 positions in two rows give a high circuit count for the board area, suited for parallel data buses or LVDS links in camera modules, display interfaces, or battery management boards.
That dimension is the total board-to-board spacing when the pair is fully seated — critical for enclosure design where the gap between stacked PCBs is fixed. The 0.053" (1.35mm) height above board of the receptacle alone gives a sense of the z-height budget on the bottom board. Surface-mount termination with gold-plated contacts ensures a corrosion-resistant interface for moderate-cycle applications.