The document discusses olfactory interfaces, which provide smells to users. It defines olfactory as related to the sense of smell and explains that olfactory interfaces generate and deliver smells. Some advantages mentioned are reducing stress, enhancing memory, and changing mood subconsciously. Challenges include difficulty digitizing smells and conditions like anosmia (lack of smell) or hyperosmia (extreme sense of smell). Examples of olfactory interfaces discussed are "Smell-O-Vision" movies, NASA's "E-Nose" device, and products that simulate smells like flowers or burning rubber. The future of olfactory interfaces may include uses in security and gaming.