Often refers to the 4-pin connectors used to attach DC power to the drives inside a PC cabinet. Molex is a large manufacturer of electronics plugs and sockets that dates back to the 1940s.

There's also SATA power cables in straight or right-handed connectors, depending on the orientation inside your PC chassis, and a PATA cable in case you have any Molex-needing components like ...

Molex’s MMCX PoC connectors deliver signal integrity and power delivery improvements over traditional MMCX connectors.