The term "kief" has been used for the powder made from glands (sometimes termed trichomes) that have been sifted or rubbed from the buds and leaves of the plant.
In North America and Europe, kief is also described as the glands of the mature female plant.
Kief powder refers to this loose collection. It can pressed to make hash using presses with heated iron or plates, although this is not the only method by which hash is made. In the US kief is sometimes pressed into hash, but it is more likely to be smoked or vaporized alone or used to top some bud in a pipe.
Kief can be collected by rubbing leaves or buds over a fine silkscreen or stainless steel mesh screen. The glands are pulled from the vegetative material and drop through the screen to be collected.
The Pollinator, invented by Holland's Mila Jansen, revolutionized kief making. Large amounts of leaf can be processed with little human labor. The machine consists of a box enclosing a rotating drum made from silk or stainless mesh. As the drum rotates the leaf tumbles against the mesh and glands fall off.
Kief is prized because of its high concentration of glands and its smoothness when it is inhaled. Needless to say, there are many qualities of kief depending mostly on the qualities of the marijuana that was screened. Like olive oil pressing, the screening process is also a major determinant of quality.