priority mail usa is one of USPS’s fastest domestic shipping services, offering delivery within 1-3 business days. It includes features such as tracking, insurance up to $50, and the option for delivery to a PO Box. Priority Mail is often used for packages that need to arrive quickly but do not require the next-day urgency of Priority Mail Express. USPS also offers flat-rate options for Priority Mail, where the cost remains the same regardless of the package weight (up to a certain limit), making it a cost-effective solution for heavy items within the U.S.