Website that allows users to submit and vote on content, as well as visit and create "subreddits" for individual topics/events/groups, etc. Users can comment on submissions, and upvote/downvote each other's comments too. You can see user's comment history and "karma score", which is how many points they have collected from submitting content and votes others have given their comments, by clicking a person's username. E.g. http://reddit.com/user/USERNAME
Comments can be rude and often NFSW (Not Safe For Work), so can content (although users are given the option of tagging content as NSFW, which adds a red "NSFW" tag in a box under the submission).
Website is safe, no malicious content or viruses, though some tracking cookies are present, such as Google Analytics.