Goods are items that are usually (but not always) tangible, such as pens, physical books, salt, apples, and hats. Services are activities provided by other people, who include architects, suppliers, contractors, technologists, teachers, doctors, lawn care workers, dentists, barbers, waiters, online servers, a digital book, a digital video game or a digital movie. Taken together, it is the production, distribution, and consumption of goods and services which underpins all economic activity and trade. According to economic theory, consumption of goods and services is assumed to provide utility (satisfaction) to the consumer or end-user, although businesses also consume goods and services in the course of producing other goods and services (see: Distribution: Channels and intermediaries).