ACH is the network US banks use to move money electronically between accounts. For distributors it is a cheaper way than cards to collect customer payments, and a common way to pay suppliers.
ACH payments can be returned after they appear to succeed, for example for insufficient funds, so a system that accepts ACH needs a way to reverse a payment and flag the account when a return comes back.
APFoodz accepts ACH through CardPointe and GoodFunds, and a returned payment is reversed for you.