For example, during a very long period, say ten or twenty years, excess supply of money in many cases corresponds to rises in prices while short supply does to price declines. This is quite natural in light of the fact that prices are the rate of exchange between goods/services and money.
Based on this long-term relationship between prices and money, price fluctuations are referred to as essentially monetary phenomenon and price stability is considered to be the objective of monetary policy. During a shorter period, say a few months or a few years, however, price fluctuations are influenced by not only money but also a variety of other variables.