Time to maturity
How much time is left until the principal comes back.
How to read the number
It sets the upper bound of the horizon: whoever holds to maturity receives par regardless of what the price did along the way.
When the metric lies
For amortising issues and issues with a put date the figure misleads: cash returns earlier, and comparing such a bond with a plain one by maturity date is not a comparison.
Also known as: tenor, remaining term