A swap is an agreement between two counterparties to exchange cash flow streams, such as interest payments or currencies. The main types of swaps discussed are interest rate swaps, currency swaps, and forex swaps. An interest rate swap involves exchanging interest payments, such as a fixed rate for a floating rate. A currency swap exchanges principal and interest payments in different currencies. A forex swap is an agreement to buy one currency now and sell it back in the future at an agreed upon exchange rate.