True Miles Unknown (TMU) is the more polite cousin of its far more blunt and plain-spoken relative, Not Actual Miles (NAM). These two terms are used to describe a car that had one of a few different tragic events happen to it.
Often seen in classified advertisements in abbreviated form, TMU and NAM mean exactly what they spell out: that mileage history is a big fat question mark. It could have only 83,000 miles, or it could have 283,000 miles. Your guess is as good as the homework you do. That homework starts with the vehicle history (CarFax, AutoCheck, or publicly available records) but even then, you can be stuck.
