The taxonomy hidden list contains all the metadata taxonomy terms that are used in your site collections. Below are some of the facts about this list:
a. As the name of the list indicates, the list is a hidden list which means you will not be seeing a link to this list anywhere in your site collection.
b. The URL of the list would be like: http://YourSharePointSite/Lists/TaxonomyHiddenList/
c. This list will only be present in the root site of your site collection.
d. The list by default has read access to all NT\Authenticated users. Make sure to verify this when your users have issues with using the metadata taxonomy service.
e. The list contains only the taxonomy terms that were actually used anywhere in your site collections. That means when you are using a taxonomy term for the first time in any list, that term gets added as a new list item in the taxonomy hidden list.
f. This list contains the following fields to store the data about the taxonomy terms: