Here's the biggest offenders I see when talking to founders: revenue vs GMV (if you give GMV, give me your cut/margin) contract vs LOI burn vs expenses users vs customers (customers pay) signups vs users vs active users (you should give active with time interval and measurement of active. eg. logged in last 30 days) profitable vs cash flow positive Others people should know: diff between retention rate vs churn rate…
For those who didn't realize the difference between expenses and burn (I'd always equated them): "Your burn rate is the speed at which your cash balance is going down." http://avc.com/2011/12/burn-rate/
Generally speaking, if you have no revenue then burn == expenses.
So for the period during which most founders are starting to learn about these terms, "burn" and "expenses" are indistinguishable. That tends to cause them to think of them as essentially the same thing for far longer than they should.