A social networking service (also social networking site or social media) is an online platform which people use to build social networks or social relationship with other people who share similar personal or career interests, activities, backgrounds or real-life connections.

The social network is distributed across various computer networks. The social networks are inherently computer networks, linking people, organization, and knowledge. Social networking services vary in format and the number of features. They can incorporate a range of new information and communication tools, operating on desktops and on laptops, on mobile devices such as tablet computers and smartphones. They may feature digital photo/video/sharing and “web logging” diary entries online (blogging). Online community services are sometimes considered social-network services by programmers and users, though in a broader sense, a social-network service usually provides an individual-centered service whereas online community services are group-centered. Defined as “websites that facilitate the building of a network of contacts in order to exchange various types of content online,” social networking sites provide a space for interaction to continue beyond in person interactions. These computer mediated interactions link members of various networks and may help to both maintain and develop new social ties.

Social networking sites allow users to share ideas, digital photos and videos, posts, and to inform others about online or real-world activities and events with people in their network. While in-person social networking – such as gathering in a village market to talk about events – has existed since the earliest development of towns, the web enables people to connect with others who live in different locations, ranging from across a city to across the world. Depending on the social media platform, members may be able to contact any other member. In other cases, members can contact anyone they have a connection to, and subsequently anyone that contact has a connection to, and so on. The success of social networking services can be seen in their dominance in society today, with Facebook having a massive 2.13 billion active monthly users and an average of 1.4 billion daily active users in 2017. LinkedIn, a career-oriented social-networking service, generally requires that a member personally know another member in real life before they contact them online. Some services require members to have a preexisting connection to contact other members.

The main types of social networking services contain category places (such as age or occupation or religion), means to connect with friends (usually with self-description pages), and a recommendation system linked to trust. One can categorize social-network services into four types:

• socializing social network services used primarily for socializing with existing friends (e.g., Facebook)
• online social networks are decentralized and distributed computer networks where users communicate with each other through internet services.
• networking social network services used primarily for non-social interpersonal communication (e.g., LinkedIn, a career- and employment-oriented site)
• social navigation social network services used primarily for helping users to find specific information or resources (e.g., Goodreads for books)

There have been attempts to standardize these services to avoid the need to duplicate entries of friends and interests (see the FOAF standard). A study reveals that India recorded world’s largest growth in terms of social media users in 2013. A 2013 survey found that 73% of U.S. adults use social-networking sites.