What's the difference between 'Total orders placed' and 'Orders' in sales reports?

Can you explain the difference between “Total orders placed” and “Orders”?

The former is a column you get when you export a sessions report. (Note that in the website it is called ‘Sessions converted’, but in the export file it is labelled ‘Total orders placed’).

The latter is a selectable column in the sales report.

For us, Orders is 3x the number of Total orders placed. I’ve seen elsewhere a suggestion that a difference can be driven by a customer making multiple orders in a single session, but having checked this is a very rare event for us, and nowhere near frequent enought to explain our 3x difference.

Thanks very much for your help