Reddit (; stylized in all lowercase as reddit) is an American social news aggregation, content rating, and discussion website. Registered users (commonly referred to as "Redditors") submit content to the site such as links, text posts, images, and videos, which are then voted up or down by other members. Posts are organized by subject into user-created boards called "communities" or "subreddits". Submissions with more upvotes appear towards the top of their subreddit and, if they receive enough upvotes, ultimately on the site's front page. Reddit administrators moderate the communities. Moderation is also conducted by community-specific moderators, who are not Reddit employees.

As of February 2023, Reddit ranks as the 10th-most-visited website in the world and 6th most-visited website in the U.S., according to Semrush. About 42–49.3% of its user base comes from the United States, followed by the United Kingdom at 7.9–8.2% and Canada at 5.2–7.8%. Twenty-two percent of U.S. adults aged 18 to 29 years, and 14 percent of U.S. adults aged 30 to 49 years, regularly use Reddit.

Reddit was founded by University of Virginia roommates Steve Huffman and Alexis Ohanian, with Aaron Swartz, in 2005. Condé Nast Publications acquired the site in October 2006. In 2011, Reddit became an independent subsidiary of Condé Nast's parent company, Advance Publications. In October 2014, Reddit raised $50 million in a funding round led by Sam Altman and including investors Marc Andreessen, Peter Thiel, Ron Conway, Snoop Dogg, and Jared Leto. Their investment valued the company at $500 million then. In July 2017, Reddit raised $200 million for a $1.8 billion valuation, with Advance Publications remaining the majority stakeholder. In February 2019, a $300 million funding round led by Tencent brought the company's valuation to $3 billion. In August 2021, a $700 million funding round led by Fidelity Investments raised that valuation to over $10 billion. The company then reportedly filed for an IPO in December 2021 with a valuation of 15 billion dollars.

Reddit has received praise for many of its features, such as the ability to create several subreddits for niche communities, being a platform for raising publicity for numerous causes, and has grown to be one of the most visited websites on the Internet. However, it has also drawn negative attention for its propensity to spread potentially dangerous misinformation.