Audit Trail

The most tedious hike on the Pacific Crest Trail. Also, a series of accounting records that allow people to follow how money has been spent.
It may seem relatively obvious where money gets spent. In a large company, though, the way funds get distributed sometimes becomes murky. To keep tabs on everything, a system of documentation is put in place, making sure a paper trail exists that the accountants can follow later. This documentation is known as the audit trail, or sometimes the audit log.
Here's a quick example: you take a flight for a business trip. The audit trail for the flight might be the ticket confirmation, the statement from your company credit card showing the purchased ticket, the approval from your supervisor, and maybe some info about where you were going.