Price stability refers to the stability of the overall price level, measured, for example, by the price index for overall output (the chain-weighted price index of GDP) or for consumer goods and services (the Consumer Price Index). We often satisfy ourselves with the norm of low and stable BIS Review 23/1998  -2inflation.
At any rate, price stability is really more an intermediate goal than an ultimate objective. The reason we care about price stability is that we believe that it contributes to a high and rising level of living standards. Indeed, it is viewed as so important in this regard that we identify it as a separate and free-standing norm.