4chan is described as an English-language image-board website. Essentially it is an online forum where users are able to post anonymously and search for specific content.
Users do not need an account or a username and so it is difficult to establish a social relationship using the site unless someone shares contact information. Content which has been posted (threads) expire after a certain amount of time.
The site explains that there are bulletin boards dedicated to a variety of topics from Japanese animation and culture to video games, music and photography. There are also boards for adult and NSFW (not safe for work) content.