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A chirp (in some contexts called a sweep signal) is a short burst of signal that rises or falls in frequency over the length of the burst. Radar and sonar can use chirps so the echoed signal includes information about an object's reflectivity over a range of frequencies. Radar on planet-orbiting probes may send chirps to yield information on the ground's reflectivity and transparency at different frequencies, revealing information about the planet's surface material and structure.
The term chirp is used for the gravitational wave signals from compact object mergers that are discernible within data collected by gravitational-wave detectors (such as LIGO) because they fit this description: the appearance of a distinct frequency that increases, then ends abruptly.