Rapid, very large price increases constitute hyperinflation.
Hyperinflation is extremely rapid or out of control inflation. There is no precise numerical definition to hyperinflation. Hyperinflation is a situation where the price increases are so out of control that the concept of inflation is meaningless.
When associated with depressions, hyperinflation often occurs when there is a large increase in the money supply not supported by gross domestic product (GDP) growth, resulting in an imbalance in the supply and demand for the money. Left unchecked this causes prices to increase, as the currency loses its value.
When associated with wars, hyperinflation often occurs when there is a loss of confidence in a currency's ability to maintain its value in the aftermath. Because of this, sellers demand a risk premium to accept the currency, and they do this by raising their prices.
Hyperinflation affects almost everyone, therefore it's hard to avoid. But you can take some steps to minimize its effects. See Money Morning's The Three Steps to Avoiding Hyperinflation to find out how.