Mass delete is a feature which supports deletion of multiple Jira configurations at once, e.g. Issue type schemes or inactive workflows.
As of now, the bulk delete operation just works for unused (e.g. unused field configurations) or inactive (e.g. inactive workflows) items in Jira.
Mass delete in detail
The following picture shows the usage of Admin Toolbox's bulk delete.
All of the above listed, supported screens display the shown toolbar with the bulk delete button.
Clicking this button will cause the deletion of all unused and inactive items.
Mass delete unused/inactive configurations
If there are items to delete, they will be listed and can be selected for deletion. By clicking on the checkbox on the top, all items in the list will be marked.
Only items that are not in use can be deleted. They must not be part of any schemes or projects.