Active and passive ULD (Unit Load Device) are two types of cargo containers used in the aviation industry.

Active

Active ULD's are temperature-controlled containers that maintain a specific temperature range through the use of built-in cooling or heating systems. This type of ULD is used for transporting perishable goods, such as food and pharmaceuticals, that require specific temperature conditions.

Passive

Passive ULD's, on the other hand, do not have temperature control systems. They are designed for general cargo, such as clothing, electronics, and other non-perishable items, and rely on the temperature of the surrounding environment to maintain temperature. Passive ULD's are generally lighter and less expensive than active ULD's.