The 2154829-3: It carries a 7A per-contact current rating at 600V, which means each pin can handle moderate power loads — think a small power distribution point on a PCB, not just a signal line. This is a bottom-entry, surface-mount header — it sits on the solder side of the board, with the pins passing through the PCB to mate with a receptacle on the opposite side.
The mounting type is Surface Mount, Bottom Entry, Through Board — the header body is soldered to pads on the bottom of the PCB, while the male pins extend through plated holes to the top side for mating. The board lock feature provides mechanical retention during the reflow process and adds vibration resistance once the connector is mated.