All air tickets have fare conditions attached to them that determine the price of the ticket. The most common conditions to be aware of are those governing whether a ticket is refundable and whether additional charges will be imposed in the event your travel plans change.
Different fares will have different conditions. A ticket that allows you to change the dates of your travel without charge, or to receive a full refund if you cancel your travel plans, will be more expensive, but it may be useful if you think your travel plans might change.
Be sure to ask your reservations agent about the fare conditions associated with the flights you are considering. If you are booking online, simply click Fare Conditions to view the rules governing a flight before adding it to your itinerary.