Resin has multiple meanings in the cannabis world. It refers to the cyrstals that are used to make hash. Resin is also a term for the sticky residue that builds up in marijuana smoking apparatuses after smoking marijuana again and again. The resin in the smoking apparatus should be scraped on a regular basis or the piece will become clogged. Once scraped the resin can be smoked but, this should be done only if the smoker has no other options as resin contains impurities and low levels of THC.