Resin

Resin is a sticky substance secreted by the trichomes of cannabis. The cannabis plant secretes this resin in order to protect the plant from UV radiation and pests. Highly resinous cannabis plants often contain high levels of cannabinoids and terpenes, making them more potent. When cannabis flower or hashish is smoked in a pipe or bong, the heat of combustion causes the resinous oil and plant matter to solidify, leaving a black residue in the bowl, also called resin. This resin can be scraped off and smoked again, but it will be significantly less effective and very harsh.