Zimbabwe suffers from inflation of about 231 million percent a year. (Roughly, 5.5% a day.) There are many reasons for this, the most obvious being that the government keeps printing money. Like other goods, the value of money depends on the interaction of supply and demand. If the world is flooded with dollars, dollars fall in value.
The traditional first step toward slowing or stopping inflation is to stop printing money. Zimbabwe's central bank had a different idea... they'll keep the presses running, but the money will be printed with a built-in expiry date.
Very clever, even if didn't work.