Answer:
it's a light dust that covers weed. It has a high THC content. Some people store their weed in a screen box, so over time while moving the weed in the box the pixie dust falls onto a removable mirrored plate below. The plate can be removed for collecting the pixie dust, which is then consumed. Probably the most popular way is scooping the pixie dust onto a bowl of weed and then smoking it.