Purge Deleted Custom Fields

Custom fields you delete from an object are removed from the object but remain in the system for 15 days until they’re hard deleted automatically by Salesforce. During that time, the deleted custom fields continue to count toward your custom field allocation. When your org reaches 75% of its custom field allocation and it has custom fields that are ready to hard delete, Salesforce displays the Purge button. You can use it to initiate the hard delete process and free up custom field allocation for your org before the hard delete takes place.