A reaction is a one-click response to indicate how users feel about something. Using reactions enables community members to provide a response to a question or comment (Like, Vote Up) without typing anything. You can earn points and badges when others react positively to your posted content.
Here's an example of a "Like" on a response to a discussion.
You can also Agree, Flag, or Quote a post.
Use reactions to engage on posts and let others know how you feel, even if you don't have anything specific to say.