In essence snowboard binding forward lean is the angle of your calf to the snowboard itself. The amount of forward lean is usually adjustable by a device located on the back of your snowboard bindings highback (the part of the binding that surrounds the back of your leg supporting it when snowboarding). Due to the lack of a high back with snowboard hard boots a built-in adjustment system is usually how you adjust the forward lean for snowboard hard boots.

The more forward lean you have on your hard boots or soft boot bindings high-back the less angle there is between your calf and your snowboard.

Snowboarding forward lean is essential for control on your heel side carves and turns. Companies have been integrating this in to the designs of their snowboard soft bindings with the use of higher, stiffer highbacks for improved control. However, for freestyle snowboarding such as in the halfpipe you are likely to prefer a smaller more flexible highback. snowboard binding forward lean also forces you to bend your knees giving you a lower center of gravity which is better for quick reactions and control.

For more control and better leverage in your heel side turns add more forward lean, however, do note that over doing it and adding to much forward lean causes your knee to bend to much putting pressure on your quadriceps muscles and can actually make it harder to turn. The key is to find a happy middle ground that feels comfortable but also gives you sufficient heel side control and response. Experiment until you feel you have right amount of forward lean.