A chirp is an electromagnetic signal pulse that changes frequency over time. If the frequency increases, it's called an up-chirp, and if the frequency decreases, it's referred to as a down-chirp. A chirp may also be called a sweep signal.
Chirps are inherently resistant to noise and interference. They have important uses in radar detection, laser optics, and wireless communications technologies. Chirp spread spectrum communications are used in some LPWAN implementations, providing low-power, low-bitrate digital communications over long distances.