Generally, inflation will occur if the money supply increases, ceteris paribus. Deflation will generally occur if the money supply is decreased, ceteris paribus.
Inflation is an increase in the general price level of the economy.
Deflation would be a decrease in the general price level of the economy. Most people think of inflation as being something bad. If your income does not increase at the same rate as inflation, then your purchasing power does decrease or erode away. If your income increases at a rate greater than inflation, then your purchasing power increases, and you are better off. Real estate has often been termed a hedge against inflation.