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 use chirps to yield information on the ground's reflectivity and transparency at different frequencies, revealing information about the planet's surface material and structure.
Frequency Modulation (FM)
Gravitational Wave (GW)