Answer
Invoice coding is assigning the correct general ledger expense account, cost center/department, and tax code to an invoice (or each line) so the cost is recorded in the right place for reporting and budgeting. For PO invoices the coding often flows from the PO; for non-PO invoices the approver or AP clerk applies it.
Non-PO invoice for marketing software, $1,200 + $120 tax:
Dr 6500 Software Expense (Marketing dept) 1,200
Dr 1360 Input VAT/Tax Receivable 120
Cr 2100 Accounts Payable 1,320Real-world example A consulting invoice is coded to account 6200 Professional Fees under the Finance cost center so it lands in the right budget line.