The "exchange rate" is the amount of one type of currency (money) that you're able to buy with another currency. The exchange rate between currencies changes daily. This can affect the prices of things that are bought and sold from other countries.
When you say what the current exchange rate is, you can say it like this:
The current exchange rate is 128 yen to 1 euro.
But in casual speech, we don't usually use the phrase "exchange rate" when saying what the rate is. Instead, we say something like this:
I read that the dollar is at 1100 won.