What major characteristic defines Man-Portable Air Defense Systems (MANPADS)?

The defining characteristic of Man-Portable Air Defense Systems (MANPADS) is their portability and concealable nature. These systems are specifically designed to be easily carried and operated by a single soldier or a small team. This feature allows for rapid deployment in various environments, making them effective against low-flying aircraft. Their compact size enables operators to conceal them, which can add a tactical advantage in combat situations.

On the other hand, options emphasizing heaviness, high cost, or extensive maintenance do not accurately reflect the fundamental purpose and design philosophy behind MANPADS. These systems are engineered for ease of use and mobility, distinguishing them from larger, more complex air defense systems that may require significant logistical support and maintenance.