Registered members submit content to the site such as links, text posts, and images, which are then voted up or down by other members. Posts are organized by subject into user-created boards called "subreddits", which cover a variety of topics such as news, politics, science, movies, video games, music, books, sports, fitness, cooking, pets and image-sharing. Submissions with more up-votes appear towards the top of their subreddit and, if they receive enough up-votes, ultimately on the site's front page. Despite strict rules prohibiting harassment, Reddit's administrators spend considerable resources on moderating the site. As of May , Reddit ranks as the 19th-most-visited website in the U. Reddit is a website comprising user-generated content —including photos, videos, links, and text-based posts—and discussions of this content in what is essentially a bulletin board system.