Twitter is an online social media and social networking service owned and operated by American company X Corp., the legal successor of Twitter, Inc. On Twitter users post or reply to texts, images and videos known as "tweets". Registered users can tweet, like, "retweet" tweets, and direct message (DM) other registered users, while unregistered users only have the ability to view public tweets. Users interact with Twitter through browser or mobile frontend software, or programmatically via its APIs.

Twitter was created by Jack Dorsey, Noah Glass, Biz Stone, and Evan Williams in March 2006 and launched in July of that year. Twitter, Inc. is based in San Francisco, California and has more than 25 offices around the world. By 2012, more than 100 million users tweeted 340 million tweets a day, and the service handled an average of 1.6 billion search queries per day. In 2013, it was one of the ten most-visited websites and has been described as "the SMS of the Internet". By the start of 2019, Twitter had more than 330 million monthly active users. In practice, the vast majority of tweets are tweeted by a minority of users. In 2020, it was estimated that approximately 48 million accounts (15% of all accounts) were fake.

On October 27, 2022, business magnate Elon Musk acquired Twitter, Inc. for US$44 billion, gaining control of the platform. Since the acquisition, the platform has been criticized for facilitating an increase in content containing hate speech. On December 20, 2022, Musk announced he would step down as CEO once a replacement had been found. As of April 2023, Musk has yet to announce a successor and remains CEO.