Just as with alpine skiing (fixed heel), a telemark binding is the means by which your boot connects to your ski. Unlike an alpine binding, a telemark binding uses a cable-and-cartridge or tray connection system that frees you to lift your heel so you can bend fully forward at the knee when you turn. This style of binding offers a distinct advantage when skinning uphill in the backcountry, and some skiers prefer to telemark at the resorts, too. How hard you ski will determine the stiffness of the cable or cartridge you need in your tele binding (swappable), and whether you want a NTN or 75mm binding. NTN or New Tele Norm utilizes a step-in tray system instead of the typical around-the-heel cable system of a 75mm or duckbill binding.
A tele binding comes in two flavors: NTN or 75mm. Most 75mm bindings won’t accept NTN boots, and potentially vice-versa. Make sure the binding you choose is compatible with the boot you want or already have.
Inbounds or Backcountry:
Inbounds telemarking doesn't require a binding that releases or one that offers a walk mode. Alternatively, if you spend at least half of your time touring in the backcountry, consider a binding with both of these features.
This refers to the tension or stiffnes of the cable or cartridge in a 75mm tele binding.
The softer the tension in the cable or cartridge, the less aggressively you can safely ski. Conversely, the greater the rigidity along the sides of your boots, the more forceful you can be when going downhill.