Inflation is the loss of purchasing power of a currency over time due to a myriad of factors including, but not limited to, over issuance of currency into the markets, unemployment, and an over dependance on debt based solutions to induce or maintain an essentially unhealthy economic growth(last one standing gets the bill).
Anecdotal Example: In 1955(ish) my dad was able to buy a movie ticket and popcorn for a quarter($0.25), last time I went, that same deal cost $15. By my admittedly shoddy math, that means that in 60 years the dollar has roughly 60 times less purchasing power in 2011 than it did in 1955. This is admittedly a weak example as there are other markets where there is less devaluation, but it's what it is.
Editorial: If things continue apace in Washington, the dollar will not even be worth printing in about 3 years and will cease to be the defacto world currency shortly thereafter. I do not know if it can be stopped.