Answer
The sales ledger (debtors ledger or accounts receivable ledger) contains a personal account for each credit customer, showing invoices (debits), and returns, receipts, and discounts (credits), and the balance owed. It's a memorandum ledger—its total is reconciled to the sales ledger control account in the nominal ledger.
Real-world example Each customer has an account in the sales ledger showing what they've been invoiced and paid.