Facebook introduced “reactions” in February 2016, rolled out in response to the virtually incessant call for a “dislike” button ever since the now-iconic ”Like“ was introduced in 2009.
The five new expressions represent Love, Haha, Wow, Sad, and Angry. These allow users to express their reactions to photos, videos, and posts in more detail—not a lot more detail, but certainly more than the a mysterious “thumbs-up.”
However, Belgium’s federal police force has warned its citizens against using the new reaction buttons.

Help define Facebook's new 'Reaction' emojis.