THC or tetrahydrocannabinol is a naturally occurring compound in the cannabis plant, known for its psychoactive effects on the human brain. However, THC also has some medical benefits such as pain relief and reducing nausea. There are various synonyms for this compound such as delta-9-tetrahydrocannabinol, delta-9-THC, or simply THC. The slang terms for THC include weed, pot, marijuana, ganja, and Mary Jane. Additionally, businesses have created brand names for THC products such as Sativex, Marinol and Syndros. While THC has both recreational and therapeutic uses, it's still illegal in many countries around the world - so be sure to check your local laws before using.