It's not a field in any of the MODX objects, so it's most likely an extra.
Check Package Manager for possible updates.
Thanks Guys - I don't have VersionX installed AndyTough - but it looks like the same issue! Odd...
The Discuss extra is also a possible culprit.
Keep in mind that some extras leave stuff behind when uninstalled, so it could be an extra you installed, then removed.