What does Macaulay duration measure?

Macaulay duration measures the present-value-weighted average time to receive a bond's promised cash flows. It is not necessarily an actual payment date. It is an average timing measure.

For a coupon bond, some value arrives before maturity through coupons, so Macaulay duration is usually shorter than maturity. For a zero-coupon bond, all value arrives at maturity, so Macaulay duration equals maturity.