P.O. Alternative is a term used to refer to private delivery services such as UPS and FEDEX, which are alternatives to the United States Postal Service (USPS). UPS is a three-letter acronym for United Parcel Service, while FEDEX is an acronym for Federal Express. Both UPS and FEDEX offer delivery services that are faster and more reliable than USPS, making them popular alternatives for those who need to send packages quickly.