Shipping and freight is a global industry, and as such, it involves trading in many currencies. US Dollar, Euro, and Pound are the most common currencies in trading.
Since each country has its exchange rate and these three main currencies fluctuate, the shipping industry had to find a way to offset monetary losses due to this fluctuation.
Currency Adjustment Factor (CAF) is a charge levied by some shipping lines on trade lanes to cover such financial losses. The quantum of CAF could be on a percentage or per container basis.
Related reading:
Terminal Handling Charges (THC) Explained