Frontside Vs. Backside
This distinction is essential to understanding freestyle snowboarding and is borrowed from surfing, which uses it to distinguish different types of waves. Because a snowboarder stands sideways on the board, turns and movements are asymmetrical; a turn on the heels looks different and requires different movements than a turn on the toes. The frontside/backside dichotomy is useful for understanding terrain and tricks, though it can be confusing.
The simplest explanation is that frontside involves turning to face down the hill, while backside involves facing up the hill; therefore a frontside turn is done on the heels, while a backside turn is done on the toes.
All rotations are either backside or frontside, as well; if one jumps and turns looking downhill, the spin is frontside, but jumping and turning one's back to the fall line is a backside spin. When applied to terrain however, the frontside/backside distinction is different; a halfpipe for instance, has frontside and backside walls. If one were to straight run down the middle of the halfpipe, the rationale would be apparent; the rider faces the frontside wall, and approaches on the toes, while backside wall is behind them and is approached on the heels.
This applies to rails and boxes as well; the method of approach determines the name of the trick, not the direction of rotation. A boardslide, executed facing up hill, is actually a frontside boardslide, because the obstacle is approached from the frontside.