Several characteristics define sound, including frequency, pitch, loudness, wavelength and period. Sound travels in waves and is caused by vibrations. Sound travels fastest through solids, slowest in gases and at an intermediate speed through liquids.
Bats and insects use a sound detection system known as echolocation to navigate their way through their environments. Echolocation is an example of a specialized sound detection system. During echolocation, a bat sends out high-frequency sound waves. An echo is returned and detected by the bat's auditory system. This method allows a bat to "see" in the dark, especially when it is looking for food.