Price-yield relationship
The basic property of a bond: its payments are fixed, so a rise in price automatically means a fall in yield, and the other way round.
How to read the number
The reaction to rates follows from this. When new issues start paying more, old ones cheapen by exactly enough to match them on yield.
When the metric lies
The relationship is not linear: for an equal move in yield the price gains more than it loses. On small moves the asymmetry is invisible; on large ones it matters.
Also known as: inverse price yield link