A soft bounce is an e-mail message that gets as far as the supporter’s mail server but is bounced back undelivered before it gets to the intended recipient. This could be an out of office autoreply, for example.
A hard bounce is an e-mail message that has been returned to the sender because the recipient’s address does not work.
A suppression is an email address that has either hard bounced, seen a number of soft bounces or received a ‘spam’ complaint. They will no longer be emailed although they will still be in your account unless they are deleted.