Simplex fiber optic cable and duplex fiber optic cable:
Simplex fiber optic patch cords are with simplex fiber optic cables, simplex means this cable is with only one thread of fiber optic glass inside the single core. And simplex cables are with one single outer jacket.
Duplex fiber optic patch cords are with duplex fiber optic cables, duplex cables can be regarded as two simplex cables having their jackets conjoined by a strip of jacket material, some duplex fiber optic patch cords are with clips on the two fiber optic connectors at each side of the cable to combine the two connectors together. Below are the pictures to illustrate what is simplex and what is duplex:

As on the picture, the left one is a simplex LC APC type fiber optic patch cord, with simplex fiber optic cable,
The right one is a duplex LC APC type fiber optic patch cord, with duplex fiber optic cable and with clips to combine the two connectors.

There are also multi fiber cables, here we compare the multi fiber cables with simplex cables: they are both with a single outer jacket, but simplex only has one thread fiber glass inside the core, while multi fiber has many threads of fiber optic glass inside the core. For example, an 8-core multi fiber cable. There are ribbon type and bundle type multi fiber cables.

Simplex and duplex are with cable structure types; they are different from single mode and multi mode, which are related to fiber optic glass types.

We are manufacturer and supplier of various kinds of fiber optic patch cords including simplex, duplex and multi fiber ones.