It's a free-hanging (in-line) female socket connector with a single row of tin-plated contacts at the standard 0.156" (3.96mm) pitch that defines the MTA-156 series. The orange housing carries a closed end — no back-loading of contacts — and a polarizing key that lines up with the matching header's keyway so you can't plug it in wrong.
This is an IDC (insulation displacement) connector, so there's no crimping or soldering at the termination end. Tin is the right call here: it's cost-effective for fixed or occasional-mate applications, and the thick plating handles the IDC wipe without galling.
The 3-643817-6 mates with any standard MTA-156 pin header — through-hole or vertical — that shares the 0.156" pitch and 6-position count. The polarizing key on the receptacle aligns with the corresponding slot on the header; if the key is missing or mismatched, the housings won't fully engage.