What does the "C" mean in "CSR" MMF optics?

Hey all, I have a curiosity I'd like to put to rest.

I recently bought some generic optics to split a 40Gb QSFP into 4x10Gb interfaces. It has an MPO-12 and each 10Gb "lane" is physically split out into a pair of those MPO fibers. IOW, the cable has MPO-12 on the transceiver end and a split of 4 LC connectors that I can plug into individual edge devices. It's pretty neat, and pretty straight forward.

Then I started to fixate on the part number having a "C" as in "CSR4" and I did some googling to calm my inquiring mind. I know what ordinary SR4 means, but what's that damn "C" about? I thought maybe it follows the same general vocab as in video applications where one combined type was "composite" (yellow RCA) or "component" (red-green-blue RCAs) but those are my best guesses.

I got extra curious when I found this Cisco datasheet which has both of these parts listed with "CSR" in them:

Cisco QSFP-40G-CSR-S (S-Class)

The QSFP-40G-CSR-S is a pluggable optical transceiver with a duplex LC connector interface used for connectivity using MultiMode Fiber (MMF). The Cisco 40GBASE-CSR Modules support link lengths of 300 and 400 meters, respectively, on laser-optimized OM3, and OM4/OM5 multimode fibers. Customers benefit through the reuse of their existing 10 gigabit duplex MMF infrastructure as they migrate to 40 Gigabit Ethernet, while maintaining the same supported link distances as 10G Ethernet. Each QSFP-40G-CSR-S operates at four different wavelengths. Each of the four wavelengths operates at 10G over existing duplex multimode fiber using standard LC connectors. The Cisco QSFP-40G-CSR-S transceiver does not support FCoE.

Cisco QSFP-40G-CSR4

Cisco 40GBASE-CSR4 QSFP Modules extend the reach of the IEEE 40GBASE-SR4 interface to 300 and 400 meters on laser-optimized OM3, and OM4/OM5 multimode parallel fiber, respectively. Each 10-gigabit lane of this module is compliant to IEEE 10GBASE-SR specifications. This module can be used for native 40G optical links over 12-fiber parallel cables with MPO/MTP female connectors or in a 4x10G breakout mode with parallel to duplex fiber breakout cables for connectivity to four 10GBASE-SR interfaces. Cisco QSFP-40G-CSR4 is optimized to guarantee interoperability over the complete specification range of 10GBASE-SR.

Does anyone know exactly what that "C" means?