A social networking service is an online service, platform, or site that focuses on building and reflecting of social networks or social relations among people, who, for example, share interests and/or activities. A social network service consists of a representation of each user (often a profile), his/her social links, and a variety of additional services. Most social network services are web-based and provide means for users to interact over the Internet, such as e-mail and instant messaging. Online community services are sometimes considered as a social network service, though in a broader sense, social network service usually means an individual-centered service whereas online community services are group-centered. Social networking sites allow users to share ideas, activities, events, and interests within their individual networks.

The main types of social networking services are those that contain category places (such as former school year or classmates), means to connect with friends (usually with self-description pages), and a recommendation system linked to trust. Popular methods now combine many of these, with Facebook and Twitter widely used worldwide, Nexopia (mostly in Canada); Bebo, VKontakte, Hi5, Hyves (mostly in The Netherlands), Draugiem.lv (mostly in Latvia), StudiVZ (mostly in Germany), iWiW (mostly in Hungary), Tuenti (mostly in Spain), Nasza-Klasa (mostly in Poland), Decayenne, Tagged, XING, Badoo and Skyrock in parts of Europe; Orkut and Hi5 in South America and Central America; and Mixi, Multiply, Orkut, Wretch, renren and Cyworld in Asia and the Pacific Islands and Facebook, Twitter, LinkedIn and Google+ are very popular in India.
There have been attempts to standardize these services to avoid the need to duplicate entries of friends and interests (see the FOAF standard and the Open Source Initiative). A 2011 survey found that 47% of American adults use a social network.