What is the difference between 'payor' and 'payer?'

"Payer" and "payor" are interchangeable spellings of the word used to describe a person or organization who gives money for some kind of goods or services. Essentially, both "payer" and "payor" mean "one who pays."

According to the Merriam Webster Online Dictionary, a payer is "a person, organization, etc., that pays or is responsible for paying something." It lists payor as a non-preferred spelling variant of the word payer. The "-or" ending is sometimes used in medical and insurance documents such as when defining or describing third-party payors and responsibilities. In legal documents payor is used to describe a person required by law to make specific payments such as child support.