The Reddit front page is where the most popular posts of the day are shown. Reddit is made up of different topic sections called "subreddits." Users post links within these subreddits, which are voted up or down by the users. The most up-voted posts are shown on the front page.
Reddit bills itself as the "front page of the Internet" because of its unique user voting system. Registered users are able to customize the subreddits they see when visiting the site. The most popular posts from those subreddits are then displayed on their front page. Unregistered users see the default front page which includes posts from more general subreddits dealing with subjects like science, education, humor and technology.