This is the number of conductors (individual wires) inside the cable. 2-Wire: Heating only (older boilers).
If you are buying wire for a (like Nest or Ecobee), do not settle for anything less than a 5-conductor cable. Learn about the common or C wire - Google Nest Help buy thermostat wire
Standard for most modern heat/AC systems. It includes the crucial C-wire . 8-Wire: Recommended for heat pumps or multi-stage systems. 2. The "C-Wire" Factor This is the number of conductors (individual wires)
The Ultimate Guide to Buying Thermostat Wire: What Every Homeowner Should Know buy thermostat wire