An ACH credit is the formal Nacha term for an ACH push payment, where the party sending money instructs its own bank to move funds into someone else's account through the Automated Clearing House network. That entry explains the mechanics in detail.
The most familiar ACH credits are payroll direct deposits, government benefit payments, tax refunds and business payments to suppliers. The payer's bank, the ODFI, sends the credit entry into the network, and the payee's bank posts it to the account on the settlement date. Because the account holder whose money leaves is the one starting the payment, ACH credits carry less risk of unauthorized use than debits.
"ACH credit" and "ACH push" mean the same thing. The term "credit" reflects how the entry is recorded at the receiving bank, while "push" describes the direction of instruction. The opposite is an ACH debit, also called an ACH pull, in which the payee draws money from the payer's account.