Powder is a term for snow that is very light and fluffy. Powder is known as being the most fun and challenging condition for skiing and snowboarding, solely because it is so soft. If powder snow sits undisturbed for too long it may become compacted and hard, sometimes icy. This is considered more difficult terrain to negotiate. Generally colder climates sport the lightest, driest powder, or "cold smoke", and countries like Switzerland are becoming known as powder havens.
In places where almost all of the runs are groomed, and powder is a rare find, you must venture into the tree trails. Powder makes for much smoother turns and smoother riding. Powder also makes for softer landings and reduced chances of injury compared to man made terrain parks, though landing in deep snow can take some practice.
Powder is best to ride when it is fresh, before other riders "track it out" and make ruts in the smooth surface. The powder snow will hold consistency if the temperature stays as cold or colder than when the snow fell, however when the sun melts it the so called "slush" is formed. This is exceptionally frustrating since it slows the board down rapidly, and if it is hit at high speed, a fall usually occurs.
Other risks with skiing or snowboarding in powder include avalanches, injuries when falling on hidden obstacles such as rocks or tree stumps snowed over, loss of equipment, and the difficulty of getting oneself out of deep powder snow after a fall.
Snowboarding in deep powder snow doesn't actually require a sharply tuned edge at all as there is nothing to 'grip' in the lightly compacted snow. However, it is preferred to have a tuned effective edge in case the terrain suddenly changes and grip is required.