__________ allow(s) a user to share ideas, activities, events and interests…

Concept: A social network service is defined by three structural elements: a user-created profile, an explicit graph of connections to other users (friends, followers, groups), and a distribution mechanism such as a feed or timeline that carries whatever a member posts along that graph. Wherever those three elements are present, the service exists so that one person's content reaches many other people.

Application: The blank has to name the thing through which a user shares ideas, activities, events and interests among people, that is, outward distribution of a person's own content to an audience of other people. Social networking sites supply all three elements: the profile records the member's interests, the connection graph defines the audience, and the feed delivers the member's posts about ideas, activities and events to that audience.

Cross-check: Compare the direction of information flow created by the other named categories:

• Adware: the flow runs from advertisers to one user's screen. It renders advertisements inside that session and gives the user no audience of other people.

• Cookies: small text files a site writes into a single browser and reads back on later requests. They carry session state such as login, cart and preferences for that one browser, and are never displayed to other users.

• Open source software: a licensing model that grants any recipient the right to read, modify and redistribute source code. What travels between people is program code among developers, not a member's ideas, activities or events.

Result: The blank is filled by social networking sites.