THC oil is technically a concentration or an extract. That implies the cannabis plant matter has been cleaned with some kind of solvent [popular solvents include isopropyl alcohol, butane, and carbon dioxide (CO2)]. When trichomes, THC, CBD, CBN, and other cannabinoids are soaked in a solvent, they dissolve in the liquid. The plant matter is removed after the soaking procedure. The solvent is removed by boiling, leaving behind an oily material containing potent THC. When high THC cannabis strains are extracted, the end product is a highly concentrated THC oil.