Source Document
Definition
A source document is the original evidence of a transaction — an invoice, receipt, bill, or bank statement. Source documents support what was recorded in the books.
Example
A bookkeeper records a $450 software bill. The source document is the vendor bill itself, which proves the amount, date, and what was purchased.
Why It Matters
Source documents are the proof behind the books. Without them, the bookkeeper is guessing. They also support tax filings and audits.