In addition to the main sessions, the workshops, and the special sessions, many conferences provide also some tutorials, usually the day before the beginning of the event or the day after the end of the event.
Computer science NIPS conference, for example, is one of these.
I've attended some of them, and I know what they are. But, if I talked with colleagues about tutorials, each of them would give a different definition of this conference aspects.
What actually are tutorials in conferences?
Are they specific lectures for young attendees of the conference?
Are they specific talks to give the guests the opportunity to explain and advertize a particular aspect of their research?
Or are they just a way to add one day to the conference schedule?