An ACH transfer moves money electronically between bank accounts through the Automated Clearing House network, the batch-processing system that handles direct deposits, bill payments, and most online rent collection in the United States. ACH comes in two directions: a credit "pushes" money from the payer's bank (like a payroll deposit), while a debit "pulls" it with the account holder's authorization — which is how autopay rent typically works.
For rent, ACH's appeal is cost and fit: transfers are cheap compared with card processing, and rent is a predictable recurring payment that suits batch settlement. The trade-offs are speed and finality. Standard ACH settles in one to a few business days rather than instantly, and a transfer that appears to succeed can still come back later as a return — insufficient funds, a closed account, or a disputed authorization — which is why rent should be treated as collected only once the window for returns has effectively passed.