Kief is the micro-sized, sticky crystals that mask the outer layer of cannabis flowers. Also commonly referred to as dry sift or pollen, because kief is produced by "sifting" cannabis or cannabis shake in an particular manner until the precious crystalline particles come off.
What makes each strain of cannabis unique in its own way is because of the kief component. Kief contains the cannabis flower's resin glands. In these glands is where all the terpenes and cannabinoids are stored. Even if cannabis didn't contain any kief, the flower component itself still contains canabinoids. However, kief's cannabinoids are much more potent than those stored inside the flower itself.