what is priority shipping usps refers to a faster shipping service offered by the United States Postal Service. Priority Mail guarantees delivery within 1-3 business days for domestic shipments, depending on the destination. It includes tracking, free insurance up to $100, and is available for both packages and envelopes. Priority Mail is an affordable yet fast shipping option for small businesses and individuals who need quicker delivery times without the expense of Express Mail. The cost is based on weight, size, and destination.