Inflation was a continuous price increase of goods and services.
In the 20th century, NASA's Project Mercury, when adjusted for inflation, cost $2.25 billion. (PIC: "Two of One")
In 2371, after taking forty flights of stairs to see Liquidator Brunt, Quark commented on what the price of an elevator ride would have been – seven strips of latinum – as an example of inflation. (DS9: "Family Business")
During the Great Monetary Collapse on Ferenginar, Quark was away and felt helpless knowing that rampant inflation and currency devaluation were affecting his home. In 2372, he assured Miles O'Brien that he knew what it was like to be unable to do anything about protecting a place you loved, comparing this situation to Miles' fears for Earth. Miles was not comforted in the least. (DS9: "Homefront")