Active and passive radar are two different types of radar systems.
Active radars actively emit signals that are reflected by an object and then received by the radar. The time it takes for the signal to return is measured to determine the distance and speed of the object.
In contrast, passive radars receive signals emitted by other sources, such as radio or television transmitters. Based on the interference or changes in these signals, a passive radar can detect objects without emitting signals itself.
Both types have their own advantages and disadvantages, such as the stealth characteristics of passive radar, which can make it more difficult to be detected by traditional active radar systems.