The 4-103765-0-25: It mates with standard 0.025" square-post receptacles, which means the board designer gets a clean, low-profile interconnect for parallel or perpendicular board stacking, or for a cable-to-board transition via a matching IDC or crimp socket.
That gold thickness is the standard for moderate cycle life — expect several hundred mates before the contact resistance drifts. The 100 µinch tin-lead post finish is a legacy solder tail coating; it wets well with SnPb solder, though lead-free wave profiles may need a flux adjustment. That covers most indoor industrial and telecom gear, but not extended automotive underhood temperatures.