The “C” is for combo. It denotes that the array has FC and iSCSI connectivity.
You will also see C8 and C8X in some cases.
“8” denotes 8Gb FC instead of 4Gb for the base included ports.
“X” denotes 10Gbe iSCSI instead of 1Gbe for the base included ports.
You can still add 8Gb FC and 10Gbe iSCSI ports beyond the base ports to a “C” model but the speed of the base FC and iSCSI ports are determined by the model identifiers.
I think that this used to mean a "combo" array: i.e. - it had both Fibre Channel and iSCSI ports on the SP.
I'm not sure if they still use that nomenclature.....