priority or first class mail refers to two different types of shipping services offered by the United States Postal Service. Priority Mail offers faster delivery times, typically within 1-3 days, along with additional features such as tracking and insurance for higher-value items. First-Class Mail is a more economical option, primarily used for letters and lightweight parcels, with delivery times ranging from 1-5 days. The choice between Priority and First-Class Mail depends on your needs for speed and budget.