It has not been seen in this country since the 1930's and it is very bad for stocks. If you were to add up the gains of just the growth and dis-inflation phases of the US economy for the past 90 years or so, the total would equal about where the market is today. What this implies is that the periods of inflation and deflation added nothing to the value of the market. Some saying market timing doesn't work, but this clearly shows that periods of inflation and deflation are times to avoid the market. Economists vary on the definitions of the different phases of the economy, but here are some of the basics.
Inflation is too many dollars chasing too few goods.
When there is a shortage of goods, but a high demand, prices go up. That is inflation. Simply put, inflation is the growth phase gone bad. When there is increasing supply of goods, but shrinking demand, prices need to be cut to attract the few dollars being spent. This cycle of increasing supply and decreasing prices continues until demand finally catches up with the supply.