They are similar, but they are not quite the same. Kief generally refers to the collected trichomes that come from grinding your weed. It is essentially a form of “dry-sift” hash, as it goes through a micron screen and is collected only through agitation. Bubble hash is also collected trichomes, but it is typically harvested using water and ice. Both products are harvested trichomes, though kief is usually of lower quality.