The term business to business simply means sales made to another business as opposed to consumers.
Although the term is applicable to a wide range of industries, it is most often used in the media sector. It is the media sector that most often supplies otherwise similar products to both consumers and businesses. For example, a magazine publisher is likely to publish both consumer magazines and trade magazines.
It is important to distinguish between consumer and business revenue streams because they follow slightly different cycles.
During the dot com boom, the abbreviation b2b was often used for business to business. It has become less popular, probably because of its association with the bursting of the bubble (after which it was sometimes said to stand for "back to banking").