An option is a period of time within which the pre-payment of a portion of the cost of a voyage must be made. Once your travel agent tenders your voyage, your agent will ask for payment of $500.00, to be paid within a couple of weeks, if you live in the US, to secure your cabin. Full payment is due usually 60 days before the ship’s departure.
If you live in Europe it is customary to be required to make a deposit equivalent to 25% of the cost of the voyage. One agent told me that it is customary in some European countries for the agent to expect payment in full once you have contracted for a voyage, even if you are required to cancel the trip.