Trichomes from Runtz buds. Kief, also known as cannabis crystals among other names, refers to the resinous trichomes of cannabis that may accumulate in containers or be sifted from loose, dry cannabis infructescences with a mesh screen or sieve. Kief is a cannabis concentrate and therefore contains a much higher concentration of psychoactive cannabinoids, such as THC, than that of the cannabis infructescences from which it is derived.