A Foreign Exchange Swap (FX Swap) is in essence an FX Spot + an FX Forward.
The FX Swap contract has two counterparts, and they agree to swap currencies with each other for a predetermined period of time, and then change back again when the period is over. By doing this, they can ensure that they both get access to the foreign currency that they need for their business transactions during a specific period of time. The FX Swap is binding for both parties.
Example: Company BBBB is based in the United States, but knows that it will be in need of AUD for its business dealings in 2017. Company NNNN is based in Australia, and knows that it will need USD for its businesses dealings in 2017. BBBB and NNNN enters into an FX Swap agreement. On January 30, 2017, 5 million USD from BBBB will be swapped for 7 million AUD from NNNN. Both parties are obliged to participate in the swap. The contract also stipulates that they will swap back again on January 30, 2018 (and this part of the contract is also binding for both parties). By using this FX Swap, both BBBB and NNNN can rest assured that they will have the foreign currency needed for 2017 and that they will also get back their native currency afterwards.
A currency swap is not the same thing as an FX Swap. With a currency swap, two counterparts swap interest rates and/or amortizing payments for loans in different currencies.