kif, kief, or keef all refer to trichrome from the bud and leaves of the marijuana plant.  I am honestly not sure of the correct spelling.  I googled it but all seem to have about the same number of results.  There are many ways of collecting kif.  The easiest and cheapest is just scrap your nug jar every now and again.  Also a lot of grinders come with a screen that allows the kif to drop down into a little compartment.  If you have a lot of trim or bud you would like to collect your kif from I would suggest checking out the DIY Pollen Sifter article.  It makes fast work of your bud.