Better late than never? The solution is perhaps a bit counter-intuitive, but you actually don't create a view of taxonomy terms:
- Create a View of [content-type] (A content type which uses your desired taxonomy).
- Add a Relationship to your taxonomy on that content type ("Content:[field-name-of-your-taxonomy]").
- Add a Filter Criterion using the Taxonomy term definition from your relationship and set the operator to "Is empty (NULL)." (At this point, we are seeing what we want, we just need to make it intuitive to view and eliminate duplicates.)
- Turn aggregation on so that each taxonomy term appears only once, even if used multiple times.
- Using an unformatted list style with fields, simply add a field for the taxonomy term name from your relationship.
- (Optional) Add a Sorting Criterion on the taxonomy term name to sort in alphabetical order.
My use case for this was having added taxonomy terms on certain pages and wanting to go back and add descriptions to the terms at a later date, after they were all done. It was helpful to have a page which only listed ones which still needed descriptions added.
Aggregation is "necessary" if you have taxonomy terms which are used on more than one different node (virtually every case). If you don't turn on aggregation, you will see one instance of the taxonomy term for every time it is used.
Thus, technically, Steps 4-6 are all optional, but the whole point of this exercise is making it easy to view taxonomy terms without descriptions.