It is possible to add tags to questions created when making a Quiz. The feature is due to be implemented at some point in the future but does not currently work. See the forum discussion https://moodle.org/mod/forum/discuss.php?d=194119
See #6 in Using tags for an explanation of course tags.
When someone adds an unsuitable or inappropriate tag, other users can click on the word (1) to get to the screen where they can flag it as inappropriate (2) The administrator can modify or delete inappropriate tags from Settings>Site administration>Appearance>Manage tags (3)