Service (economics)
Perishability (If someone doesn't use it, it is lost.) - If someone cannot sell their services, their time is "lost". It is a lost economic opportunity. For example, a doctor that is booked for only two hours a day cannot later work those hours– she has lost her economic opportunity. Other service examples are airplane seats (once the plane departs, those empty seats cannot be sold), and theatre seats (sales end at a certain point).