Authorized Recipient was not available - Certified Mail Labels

What does USPS Certified Mail tracking mean when it says 'Authorized Recipient was not available'

If an authorized recipient was not available what happens to the letter or package? Will they try again? 

USPS will attempt Certified Mail delivery several times (in most cases two times). They allow 5 to 7 days between each delivery. If the letter or package is not delivered or picked up, the item should be returned to the sender. The USPS tracking and delivery information that was recorded will provide the compliance evidence that the sender attempted to notify the person.