What are the more-advanced reply text fields called? The one that has the bold?

Sorry for being so vague but I’m not sure what the object is called I’m hoping to find a plugin for.

When someone replies to an entry of mine I want them to have “rich html”. Just like the message box here has bold, italic, link, code, etc options. I know there is a plugin out there for this but I don’t know what that is actually called* (technically it IS rich html but a search on that didn’t help much).