What do you mean by free upgrade?

Free upgrade means upgrading from the original cabin to a higher position. For example, upgrading from economy class to business class or first class, or upgrading from business class to first class, is called free upgrade. Free upgrade is sometimes because airlines engage in activities and draw lots, so free upgrade. Some economy class tickets are oversold, but there are seats in business class, so high-end passengers who buy economy class are upgraded for free, and economy class seats are available for oversold passengers. Those who can enjoy the free upgrade are members of major airlines, and the airlines will handle the upgrade requested by passengers according to the upgrade fee standard. Passengers who need special care, such as the elderly, the sick and the disabled, can be upgraded free of charge if they look for the manager's counter when checking in.