What is a Downvote on Reddit?
A downvote is an action available on Reddit, similar to a "dislike" on Youtube, in which an user downvotes a thread or comment posted by another user by pressing a downvote button with an icon of a downward arrow. The opposite action is an upvote. The total number of points a post has, the number of upvotes minus the number of downvotes, also called the karma, is displayed next to the upvote and downvote buttons.
On Imgur
Imgur also has a concept of downvotes, just like Reddit.