A more thorough explanation:

A port of call is a place where a ship stops during a voyage. It can be a harbor where ships load and unload cargo or any place where persons and cargo are allowed to enter a country and where customs officials are stationed.

• Foreign port: A port that is exclusively within the jurisdiction of another country or state.
• Free port: A port located outside a country's customs frontier, where goods may be delivered without being subjected to customs-control procedures.
• Home port: The port where a vessel is registered or where its owner resides.
• Port of delivery: The port that is the terminus of any particular voyage and where the ship unloads its cargo.
• Port of departure: The port from which a vessel departs on the start of a voyage.
• Port of destination: The port at which a voyage is to end, including any stopping places at which the ship receives or unloads cargo.
• Port of discharge: The place where a substantial part of the cargo is discharged.

For example, if a ship is traveling from New York to London, New York would be the port of departure and London would be the port of destination. Along the way, the ship may stop at other ports of call, such as Halifax or Dublin, to load or unload cargo or passengers.

Another example is a free port, such as Hong Kong. Goods can be delivered to Hong Kong without being subjected to customs-control procedures, making it an attractive location for international trade.

Overall, a port of call is an important part of a ship's voyage, allowing it to load and unload cargo, take on supplies, and allow passengers to embark or disembark.