A permanent category is a group of email addresses that you want to keep together all on the same recipient list. To create this, you can go to Contacts > Categories, choose name and description and click save. Once you've done this, import your CSV and on the last page of the import, place a check mark next to the category you want to put the contacts in.
Temporary categories are good for 30 days from the last time a campaign was sent to the specific category. For instance, if you choose to send to that temporary category on the 29th day, the expiration date will extend another 30 days. If it's not sent to for 30 days, it's deleted from the system.
This is good for one time sends. To create this, import your CSV and on the last page of the import screen, select the create category checkbox and type in a name. Select Yes for Category Expires.
1. Contacts cannot be manually added or removed from temporary categories.
2. You cannot change a temporary category into a permanent category natively in the UI. Instead, export the temporary category and re-import as a new category that does not expire.