What does it mean when one currency is falling against another currency?

That means that in the exchange market, that currency is losing value when exchanged for the other currency.
Here is an exchange table showing the value of the American dollar when compared to other currencies. When that value drops, it is said to be falling.

http://www.x-rates.com/d/USD/table.html

When one currency is falling against another currency, it means that the value of the first currency is decreasing relative to the value of the second currency in the foreign exchange market. To determine if a currency is falling against another currency, you can look at exchange rates.

Exchange rates indicate the ratio at which one currency can be exchanged for another currency. If the exchange rate between two currencies decreases, it means that it takes more units of the first currency to buy one unit of the second currency. This indicates a decrease in the value of the first currency relative to the second currency, and is commonly referred to as a currency falling or depreciating against another currency.

One way to track exchange rates is by using a foreign exchange website or financial portal that provides up-to-date exchange rate information. For example, you can visit websites like X-rates.com or OANDA.com. These websites display exchange rate tables and charts that show the value of one currency against another. By following these tables and observing changes in the exchange rates, you can determine if a currency is falling or rising against another currency.