The Taxonomy field type allows users to set their own terms for a custom user taxonomy registered for the site.
For example, your site uses a User Category taxonomy to categorize users. You can use the taxonomy field to get users to categorize themselves either at registration or in their account.
When you create the Taxonomy field, you have to choose the taxonomy (this requires some user taxonomies registered on your site)
You can also choose the ‘Field Type’ that will control how the taxonomy field displays the terms for users to select. The field types available are dropdown, multi-select and checkboxes.