Social media are new media technologies that facilitate the creation, sharing and aggregation of content (such as ideas, interests, and other forms of expression) amongst virtual communities and networks.[1][2]

Wikipedia.

The earliest forms of social media appeared almost as soon as technology could support them. E-mail and chat programs debuted in the early 1970s, but persistent communities did not surface until the creation of the discussion group network USENET in 1979.

Encyclopedia Britannica.

websites and computer programs that allow people to communicate and share information, opinions, pictures, videos, etc. on the internet, especially social networking websites

Cambridge Dictionary.