Resin is the tar-like, dark residue that remains in the pipe or bong after smoking several times without cleaning. The gunk that remains in the glassware contains tar, ash, carbon, and small amounts of THC and other cannabinoids. This type of resin can simply be called pipe resin or bong resin. This type of resin is commonly mistaken to mean the same thing as marijuana resins derived from cannabis plant material. The major reason for this mistake is because both can be called resins.