The difference is that, in a deflation  2  A mere decrease of prices of some categories of goods, in individual sectors or in certain regions should also not be termed deflation.
In a market economy, such relative price adjustments are a response to changes in supply and demand – for example differences in sectoral productivity developments – and are essential for an efficient welfare-enhancing allocation of resources. Deflation per se only occurs when price declines are so widespread that broad-based indices of prices register ongoing declines.