A sustained rise in the general level of prices — equivalently, a fall in the purchasing power of money — and one of the most politically charged forces in economic life. Inflation silently transfers wealth between creditors and debtors, erodes savings, and has toppled governments; controlling it became the defining mission of modern central banking.
In 1923 Germany, people carried cash to the bakery in wheelbarrows. Not because bread had become expensive in the ordinary sense. The money itself had stopped meaning anything. The German mark, once treated as ordinary money, was losing value so fast that a loaf could cost far more by the time you walked to the shop. Wages were paid twice a day so workers could spend them before prices jumped again. Inflation had not just raised prices. It had destroyed the thing that made prices possible — trust in money itself. That catastrophe is the extreme case. But it shows, in concentrated form, what inflation always does at any speed: it changes what your money is worth.