network externalities

Network externalities or network effects refers to the way that human social and professional networks affect the perceived value of goods, especially digital products and services. It occurs when one person's use of a product makes the product more valuable to another person. This might be for reasons of communication, for example social media or early phone use. It may also arise due to the need to exchange data or documents, for example, if one person in a work team uses a particular word processor it is often easier for others to do so as well.

Network effects are an externality in the sense used in economics, because the provision of a service to one person has an impact beyond the immediate transaction.