A social networking service is a platform to build social networks or social relations among people who, for example, share interests, activities, backgrounds, or real-life connections. 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, pictures, posts, activities, events, and interests with people in their network.

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 American-based services such as Facebook, Google+, tumblr and Twitter widely used worldwide; Nexopia in Canada;Badoo, Bebo, VKontakte, (mostly in Latvia), Hi5, Hyves(mostly in The Netherlands), iWiW (mostly in Hungary), Nasza-Klasa, Soup (mostly in Poland), Glocals in Switzerland, Skyrock, The Sphere, StudiVZ (mostly in Germany), Tagged, Tuenti (mostly in Spain), and XING in parts of Europe; Hi5 andOrkut in South America and Central America; Mxit in Africa; and Cyworld, Mixi, Orkut, renren, weibo and Wretch in Asia and the Pacific Islands.

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 networking service.

One other use that is being discussed is the use of social networks in the science communities. Julia Porter Liebeskind et al. have published a study on how new biotechnology firms are using social networking sites to share exchanges in scientific knowledge. They state in their study that by sharing information and knowledge with one another, they are able to "increase both their learning and their flexibility in ways that would not be possible within a self-contained hierarchical organization." Social networking is allowing scientific groups to expand their knowledge base and share ideas, and without these new means of communicating their theories might become "isolated and irrelevant".

THE STRUCTURE OF INPUT BIG DATA: API applications to social networks