The pure form of THC
Kief actually consists of an accumulation of the crystals that have fallen off marijuana. I have also heard it referred to as "thunder powder." Ideally it should look like a fine granular light green powder (hence the second name).
If you grow weed,you probably already know what this is. But if you are looking to get into the horticulture game, make sure that when you dry your buds that you do so on a grate with tin foil laid out underneath. This will have two effects. First your pot will dry more evenly, and not get that moldy ammonia smell (the scourge of dank nugs). Second, as the dope dries a certain amount of the crystals will fall off on to the tin foil, and can be collected at a later date.
You can also harvest some kief from the grass you already bought. To do this keep your kind shit in a plastic baggie. I know how distasteful this is to all of you would be hippies and your precious glass jars. But if you do keep your killers in a zip-lock, over time it will naturally break down to shake, and when you have finished it, there will often (if it was kind to begin with) be a sort of filmy residue in the bag. Then put your baggie in the freezer, (I don't know why... it just works... probably has something to do with chemistry), leave the bag in the freezer for a couple of days, and then you can scrape the inside. This will yield a surprisingly large amount of kief.
Once you have some kief you can smoke it (a little sprinkled over a bowl will go a long way!!!). It also is a great food additive, but you have to go through the whole sautéed butter routine, 'cause THC is lipid soluble.
IT WILL MAKE YOU STUPID, but will also make you so high you trip face, and bring you down so softly you won't even notice.