An herb grinder

An herb grinder (or simply, a grinder) is a cylindrical device with two halves (top and
bottom) that separate and have sharp teeth or pegs aligned in such a way that when both
halves are turned, material inside is shredded. Though ostensibly intended for use with
herbs and spices for cooking, they're more commonly used to shred marijuana, resulting
in a product that can be more easily hand-rolled into a "joint" that burns more evenly.
Herb grinders are typically made of either metal or plastic and come in a variety of
colors and polished metals.

Some grinders have two or three compartments instead of just one, with fine screens
separating the bottom compartments from the ones above, thus allowing the marijuana
trichomes, also called kief, to be collected separately.