In plain words
ACH (Automated Clearing House) is the U.S. network banks use to move money between accounts in batches. Direct deposits, bill autopay and most loan-app repayments run on it.
Why it matters
When you give a loan app your bank details, you usually authorize ACH debits. That lets the lender take payments automatically on set dates. If your balance is too low, the debit can fail, and both the lender and your bank may charge a fee.
Example
Illustrative example: You borrow $200 through an app and agree to repay $215 on your next payday. On that date the lender sends an ACH debit for $215. If only $150 is in your account, the debit may be returned unpaid, and you could face a returned-payment fee from the lender and an NSF fee from your bank.
Always read the term in the context of your own agreement and local law.
Related terms and guides
Pre-authorized debit · Default · Late and returned-payment fees