Next day airs, or overnight shipping, refers to the process of sending a package or document from one location to another within a day's time. Synonyms for next day airs include express shipping, same-day delivery, expedited shipping, and overnight delivery. These terms are often used interchangeably, but each may have specific requirements or limitations, such as cut-off times for delivery, weight or size restrictions, and delivery ranges. Shipping companies and logistics providers may offer variations of these services, such as morning delivery or guaranteed delivery times, to meet the needs of customers who require fast and reliable shipping.