Echo

Typical examples are the echo produced by the bottom of a well, a building, or the walls of enclosed and empty rooms.

[2] Echo in Greek mythology was a mountain nymph whose ability to speak was cursed, leaving her able only to repeat the last words spoken to her.

Some animals, such as cetaceans (dolphins and whales) and bats, use echo for location sensing and navigation, a process known as echolocation.

The echo strength is frequently measured in sound pressure level (SPL) relative to the directly transmitted wave.

They can travel undeviated through a long distance, confined to a narrow beam, and are not easily absorbed in the medium.

[citation needed] In the medical field, ultrasonic waves of sound are used in ultrasonography and echo cardiography.