Facebook is an American online social media and social networking service company based in Menlo Park, California. Its website was launched on February 4, 2004, by Mark Zuckerberg, along with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dustin Moskovitz and Chris Hughes.
Twitter is an American online news and social networking service on which users post and interact with messages known as “tweets”. Tweets were originally restricted to 140 characters, but on November 7, 2017, this limit was doubled for all languages except Japanese, Korean, and Chinese.
Instagram is a photo and video-sharing social networking service owned by Facebook, Inc. It was created by Kevin Systrom and Mike Krieger, and launched in October 2010 exclusively on iOS.
LinkedIn is a business and employment-oriented service that operates via websites and mobile apps. Founded on December 28, 2002, and launched on May 5, 2003, it is mainly used for professional networking, including employers posting jobs and job seekers posting their CVs.