Kief is a collected amount of trichomes that have been separated from the rest of the marijuana flower. Since trichomes are the sticky crystals that contain the vast majority of the plant's cannabinoids, kief is known to be extremely potent. Kief is sometimes mistakenly referred to as pollen and is the primary ingredient in hashish production.
Kush refers to a line of cannabis plants that hail from the Hindu Kush mountains in Afghanistan and Pakistan. Kush strains are indicas and have a unique aroma that have given them a large fan base. Specific breeds and plants are unique, but their aroma is generally described as "earthy" and often piney combined with citrus or sweet.