So, you know how you can react to a topic with various emojis:
There are currently only seven usable reactions; it would be cool if you could choose your own reaction rather than the pre-set ones, so there would be a little menu to search for an emoji to react with.
I’m pretty sure it only has those few because whoever set this up didn’t want people giving negative feedback (thumbs down, angry face, etc.) to people, and so they made it so only the positive ones were on there.