Perishable – in that once it has occurred it cannot be repeated in exactly the same way. For example, once a 100 meters Olympic final has been run, there will not be another for 4 more years, and even then it will be staged in a different place with many different finalists. You cannot put service in the warehouse, or store in your inventory. An interesting argument about perishability goes like this, once a flight has taken off you cannot sell that seat again, hence the airline makes no profit on that seat. Therefore the airline has no choice but to price at peak when it sells a seat at busy times in order to make a profit. That’s why restaurants offer vouchers to compensate for quieter times, and it is the same for railway tickets and matinees in Broadway during the middle of the week.